O2 or CO2

Asphyxia, compliments of Wikipedia. That is pretty much the truth.

Both I would think are true. Its easier to say "ran out of oxygen." Perhaps that is why the media says it that way.

You are describing too different situations.

One when trapped your body is depleting the oxygen and replacing it with CO². Which one will kill you first the lack of oxygen or high CO² levels of the blood. Every one is different so could go either way. All depends on ones tolerance for increased CO² of the blood. Either way your dead. The media is trying to reduce the confusion that the public would have from Carbon Monoxide

The other situation air with high CO² levels even with good oxygen levels 5% is toxic. In air at this level the body can not rid the blood of it.

Therefore, you die from the increased level of CO2 since even if there is still some O2 left, it will be too low to help you stay alive !!?

No. Only at somewhere between 10% and 15% does CO2 become a narcotic, causing you to lose consciousness. In the presence of a normal O2 level that is survivable. In the presence of a non-survivable level of O2 it will hasten your demise.

If your "small air-tight place" starts out with a normal atmosphere, then it will be ~80% nitrogen and a little less than 20% oxygen plus a few rarer gases that won't play a significant role in your scenario. Oxygen is what your brain needs to function and nitrogen is a harmless diluent. As you breathe, you will consume only the oxygen as your body has no need for nitrogen. When you exhale, you expel the nitrogen and some carbon dioxide produced by your metabolism. The nitrogen level in your small space will not change, but the CO2 level will increase as the oxygen level decreases. As the CO2 is much heavier than either oxygen or nitrogen, much of it will accumulate on the floor. So, unless you have your nose and mouth on the floor when you inhale, you will not aspirate much of the accumulating CO2, but you will get less and less oxygen until you lose consciousness. Maybe then, you will begin to aspirate more CO2 which might be enough to kill you if you weren't already dead from lack of oxygen. Lack of oxygen is a quicker killer than a surplus of CO2.

'....or one of those pesky Coasties!.....'

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Hey! Using the term 'Coasties' is derogatory.

Puddle Pirates deserve to be acknowledged for the important purpose they serve.

Someone has to staff the little boats to courageously engage the armada of wandering inflatable and makeshift rafts.

On a tangent, someone recently attempted to convince me that gambling casinos especially in Las Vegas increase the amount of oxygen in the air from the standard 20.9% to some unknown higher level. He indicated it made people feel "euphoric" and more comfortable losing their money. I think it is hogwash---anyone ever heard of this?

Thanks,

That would be likely to create a significant fire hazard. The accompanying liability is probably sufficient to suggest this is not something that is practiced.

It is more likely to result from the number of people with oxygen tanks sitting at the slots chucking quarters and "passing gas" around.

What i was taught in senior secondary school is.

1) CO2 carbon dioxide is not toxic Gas. CO or carbon monoxide is.

2) O2 Oxygen is needed to keep you alive.

3) I would not be killed if I have continues supply of oxygen minus toxic gases.

4) Carbon dioxide in pure form is not toxic.

5) Lack of oxygen kills not abundance of carbon dioxide.

What kills you is the depletion of oxygen. A high CO2 level is surprisingly well tolerated, resulting mainly in overbreathing (an attempt to clear the CO2), a rise in pulse rate and a rise in blood pressure. Indeed, in an earlier era it was thought therapeutic in some situations to add 5% CO2 to oxygen ("Carbogen") to encourage the deep breathing. The most extreme example I have ever had to look after was when some unknown individual filled a nitrous oxide cylinder with CO2. The anaesthetist administered what she believed to be 30% oxygen/70% nitrous oxide. The next 10 minutes were rather exciting. As a physiology student I have personally experienced (monitored by my supervisor) both oxygen depletion and CO2 accumulation separately. An atmospheric concentration of 18% is still sufficient to maintain life, but dropping below that acutely results in coma and ultimately death.

'....When someone is trapped in a small air-tight place, do they perish from a lack of oxygen or from carbon dioxide poisoning?....'

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This is an example of fallacy of exhaustive hypotheses, because it implies a choice must be made between the only two alternatives noted. In fact, there are other alternatives, one of which is a better answer than either of the two listed.

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A person in a small airtight container is likely to perish from the combined effects of high CO₂ and low O₂.

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Check out this paper found at the EPA website. It shows CO₂ concentrations as low as 7% can result in unconsciousness in a few minutes.

Unconsciousness essentially ends the chances of success for any acts of self preservation.

Additionally, CO₂ is responsible for most of the pain and distress associated with this type of scenario. Onset of panic not only can reduce effectiveness of any attempts to extricate ones self from the situation, but also increases the rate at which O₂ is converted to CO₂....making both situations worse.

Increased CO₂ levels may also be implicated in the onset of cardiac arrest which can stop blood flow to the brain, stopping delivery of whatever O₂ the air might still contain.

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Strong evidence for CO₂ posing a hazard beyond merely displacing O₂ can be seen in the difference between:

tolerance for O₂ concentrations down to 12%, voluntarily experienced by athletes using altitude tents;

as compared to the tolerance for CO₂ concentration as noted in the EPA paper above.

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Adding enough CO₂ to bring O₂ concentrations down from 21% to 12% would result in roughly a 40% CO₂ concentration. 40% CO₂ concentration is well above what is required to be lethal.

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I can tell you from personal experience that working in a environment with reduced O₂ down to around 17% doesn't really present a noticeable difference (though to an outside observer, I bet differences would be noticed). Submarine atmosphere is regularly maintained at reduced O₂ concentration mainly because fires are so dangerous on a sub.

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I can also tell you that the same does not hold true for increased CO₂ concentrations. When there is a problem with the CO₂ scrubbers, it becomes obvious very quickly. Everyone develops a very short fuse and behaves generally like they somehow got a lot of sand in their vag. Cranky, red faced and uncomfortable.

CO2 does many things to the human body, but being the proximate cause of death isn't one of them. When cardiac arrest occurs, the proximate cause of death is oxygen starvation, and when a traumatic event produces sufficient blood loss, the proximate cause of death is oxygen starvation. Loss of consciousness exacerbates the problem of getting oxygen to the brain, as does panic and other effects, but brain death is caused by oxygen starvation except in those cases where the brain is directly attacked, e.g., if a CO2 cylinder were to fall on your head and crush your brain, you could be said to have died of a cause other than oxygen starvation. Also true for toxins, of which CO2 is not one.

'...When cardiac arrest occurs, the proximate cause of death is oxygen starvation, and when a traumatic event produces sufficient blood loss, the proximate cause of death is oxygen starvation....'

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This is a simplification beyond the point of utility.

Consider a physician or a coroner who subscribed to your method of classifying cause of death describing the deaths of four people, one from atherosclerosis that lead to a heart attack, one from injection of potassium chloride, one who was decapitated, and one who ingested cyanide.....their professional evaluation becomes pretty useless if it is reduced to failure of oxygen to be metabolized in the brain.

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Judge (to the accused): Did you kill aforementioned deceased?

Accused (waiving his 5th): No your honor, it wasn't me! Oxygen starvation to the brain did the killing! I swear! All I did was choke and watch....I'm not the killer!

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Lets simplify it even further. Consider the following hypothetical situation:

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Being found guilty of making gross over simplification you are condemned to breathe an atmosphere of 25% O2 and 75% CO2.

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Which of the following better describes the reason you won't be making over simplification in the future:

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1. The concentration of CO2 in the atmosphere was too high.

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or

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2. The concentration of O2 in the atmosphere was too low.

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(remember, try not to oversimplify)

Well, I'm not a physician or a coroner, a judge, a juror, or even a perpetrator.

I didn't hear you claim I was wrong.

You call my method oversimplification; I prefer to think of it as deconvolution.

'...I didn't hear you claim I was wrong....'

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I think it would have been a little cruel to point it out again, since the fact had already been clearly established in Comment #13 (to which you originally responded).

Maybe, when you publish a "clearly established fact" you might dress it up a little with bold faced majescules enclosed in french braces, e.g. {PHLOGISTON}, {GLOBAL WARMING}, etc. so that the rest of us will know the discussion is over and won't muddy the waters with our petty opinions.

BTW, 75% CO2 would arrest breathing, thereby interrupting oxygen transport to the brain.

'...BTW, 75% CO2 would arrest breathing, thereby interrupting oxygen transport to the brain...'

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Case in point; as the OP asked ' do they perish from a lack of oxygen or from carbon dioxide poisoning?..' and there is no lack of Oxygen in this case (in fact there is a surplus), it is readily apparent that they perished from 'carbon dioxide poisoning' (in the hypothetical situation with 25% oxygen and 75% carbon dioxide).

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See there? You aren't relegated to only having petty opinions. You even helped demonstrate the truth of the matter. And the waters flowed clear again just after you acquiesced and stopped all that thrashing about.

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Don't be so hard on yourself.

If oxygen transport is interrupted, there could be 100% oxygen but if it's not getting to the brain, death is from lack of oxygen. Just slow down a little and think.

There is no utility attributing a cause to death if the cause of every death is attributed to oxygen not being metabolized in the brain.

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Once a description becomes so broad that nothing falls outside its bounds, it ceases to usefully describe anything.

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In a 25% O₂ 75% CO₂ atmosphere, a person does not die because of a lack of oxygen. They die because there is too much CO2.

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Hurry up a little and start thinking.

You sound like a lawyer. Pity.

CO2 intoxication causes death only inasmuch as it prevents oxygen absorption by the brain.

Whether or not it(my description) possesses sufficient utility in your scheme is unimportant.

I'm in no hurry, which is why I have time to think sufficiently for my purposes.

Don't feel bad, I once knew a lawyer who was not totally despicable.

I'm sorry to say that you have not grasped the logic. The ultimate (a better word than proximate) cause of death is that the brain cells can no longer utilise oxygen. That is always true. What appears on the coroner's certificate does not alter that truth. The cause as established by the coroner is the start of a chain of events which, it is recognised, ends in an inevitable manner by denying the brain cells of oxygen. That cause may be an interruption of the circulation, an interruption of respiration, an unsuitable atmosphere to breathe or toxins in the blood.
Just to let you know that this is not a unique logical process, I will refer you to the concept of brain death. It is now widely recognised that a combination of fairly simple neurological tests can be used to diagnose a comatose state, the distinguishing feature of which is that nobody has ever recovered from it. That is to say, when brain death has been correctly diagnosed, the rest of the body will fail (and will also cease pumping oxygen to the brain). Coroners also recognise this as the start of another chain of events which also inevitably results in death.

PHPH001 and Gene Hayes:

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Your argument that; since death always results in the brain no longer using oxygen, no longer using oxygen is the exact, necessary cause of every death, is uninformed and somewhat naive.

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No, no, I understand it must feel so good to believe you have succinctly described such a complex process, that any suggestion of the process differing from your neat explanation must certainly seem like heresy.

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I also understand that you are not alone in repeating this mantra of self assurance. It probably brings some level of comfort; at least you 'understand' this process that will bring about your demise, even if you cannot stave if off forever. That seductive draw certainly must be part of the reason so many people will vehemently defend this idea, even lacking explanations to deal with strong evidence to the contrary.

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More simply stated (since that seems to hold some particular draw for you); Your argument is remarkably similar to claiming that all automobiles meet their ultimate demise because they can't burn fuel anymore....or possibly that they can't bring oxygen to burn the fuel anymore.

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In retrospect I realize you may not see any problem with the proceeding. I'm not really sure I will have much luck communicating the important distinction between a condition always ultimately present that may have been contributory, and a condition that is always the one ultimate cause, if you are unable or unwilling to grasp that the automobile example is both problematic and isomorphic to your simplification.

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Perhaps some specific examples will help:

You wrote: '...The ultimate (a better word than proximate) cause of death is that the brain cells can no longer utilise oxygen. That is always true....'

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Consider the brain of someone who was at ground zero in Nagasaki, or Hiroshima directly exposed to the blast of Fat Man or Little Boy from directly below. Assuming the brain was vaporized in far less than a seconds time, can you understand that 'the cause of death' is not 'that the brain cells can no longer utilize oxygen'.

While it is certainly true that the brain cells can no longer utilize oxygen, it is also true that they can no longer utilize glucose, nor ponder their possible ultimate cause of demise; those things are NOT the cause of death. Those things are the result of death not necessarily the cause.

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Another way in which you may be able to see the fallacy of claiming ".._{.The ultimate (a better word than proximate) cause of death is that the brain cells can no longer utilise oxygen. That is always true.}..." is to consider the fact that life does not end right when the O₂ runs out.

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When there is insufficient O₂, cells do not just call it quits and throw in the towel. Luck for us they switch to anaerobic metabolism.

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What I am trying to allow you to see here is that 'the brain cells can no longer use oxygen' is a symptom and not necessarily a cause. Your choice of that particular process, is arbitrary because there are several other processes upon which life is critically dependent.

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Even in situations where blood flow is insufficient or insufficiently oxygenated, it is probably easier to make a solid argument that the death of the cell is caused by a number of other things:

failure of the Ion transport pump,

Depolarization of the cell,

Excess Calcium ions in the cell,

release of excess glutamate,

generation of excess phospholipases,

breakdown of cell membrane (by phospholipases),

breakdown of mitochondria.

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Any of those provide a better explanation of reason for the cells demise than 'the cell can no longer utilize oxygen'. Consider this is true even when we are talking about situations that were triggered by insufficient oxygen!

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That really should be enough (far in excess of enough really), but just for a little further reassurance consider the mechanism of reperfusion injury.

The ultra condensed version (for those who's really can't afford (or choose not) to pay that much attention) :

PHPH001 and Gene Hayes:

Given that cells resort to anaerobic processes in the absence of oxygen, a solid argument can be made that a lack of ATP is a more exact cause of the death of a cell in cases of hypoxia or anoxia, that the actual lack of oxygen itself.

That argument falls victim to the same pitfalls are your argument that all death is cause by the inability of the brain to use oxygen.....it lacks utility, since it describes something true in every case of anoxia/hypoxia.

"your argument that all death is cause by the inability of the brain to use oxygen...."

That was never my argument. Forget your agenda while reading others' posts - you can easily pick it up again.

You use a LOT of words. Try listening to them once in a while.

I do sometimes use far too many words.

Often it is when I have made repeated attempts to communicate something rather fundamental, to no avail. My reaction is to provide explanations from a couple different perspective and some examples. I make an concerted effort to be unambiguous, leaving minimal (hopefully none) conceptual or logical holes in the net, typically because the intended audience has proven to only interact weakly to the confines of reason and reality.

I know the chances are slim. I still invest the time, even though the other party makes use of the extensively defined position to pinpoint for further evaluation the exact areas of disagreement. The ultimate goal being resolution through discovering and correcting any fundamental misunderstanding that I or the other person might have, or increasing understanding of areas of determined uncertainty, for which it is clear that more than one plausible explanation currently exists. The rewards of occasional success are sufficient that I will continue to invest the time in very detailed communication.

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Mostly I receive terse dismissive (occasionally derogatory) replies, devoid of useful critique of the myriad of examples and explanations that detail my position. Often these responses will claim a (minor) discrepancy and focus on that with singular focus.

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I suspected that if I tried to respond to both you and PHPH001 in the same post, chances would be that one (or both) of you would point out a variation in wording and insist it was a grossly unfair attribution even though the difference is small and not a pivotal part of the disagreement.

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In hindsight I should have responded to you each individually.

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After all, you have now maid it clear that your argument was never 'all death is cause by the inability of the brain to use oxygen....'.

Unfortunately, you did not take that moment to succinctly express what exactly your argument IS....which would have been quite helpful.

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Instead you chose to make a snide comment about my supposed 'agenda' (which you conveniently also forgot to provide any details about what you are suggesting that might be).

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My gut feeling is that you are going to claim your position is already clearly stated. There are some inconsistencies within your responses that would keep me from agreeing with that.

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As I hope you will do for me in any future responses, I am going to specifically point out the inconsistencies I see, so that you may respond.

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Here is some of what you wrote in #15:

^{'....When cardiac arrest occurs, the proximate cause of death is oxygen starvation, and when a traumatic event produces sufficient blood loss, the proximate cause of death is oxygen starvation. Loss of consciousness exacerbates the problem of getting oxygen to the brain, as does panic and other effects, but brain death is caused by oxygen starvation ...'}

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Which, you have to admit, gives the impression that you are of the opinion that 'oxygen starvation' is pretty much always the cause of brain death.

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Right up until this next sentence... which does suggest otherwise....:

^{'...except in those cases where the brain is directly attacked, e.g., if a CO2 cylinder were to fall on your head and crush your brain, you could be said to have died of a cause other than oxygen starvation.....'}

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...and i guess my brain was just trying to smooth out some inconsistencies when I attributed to you the argument that 'all brain death is caused by the inability of the brain to use oxygen'.

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I say 'inconsistency' because if you were applying consistent logic, there is no reason why that last condition should be any different than the first three examples your mention...

....If a CO2 cylinder strikes someones skull with enough force to be lethal, using the rules you seem to be suggesting for determining proximate cause, it seems oxygen starvation would be the choice you arrive at once again.

Blunt force trauma is going to cause interruption of the flow of oxygenated blood to the brain by a number of mechanisms: direct damage to circulatory system, disruption of the autonomic nervous system's regulation of circulation or respiration, induced seizure, and swelling/pressure on the brain.

How is the physical disruption of flow of oxygenated blood to the brain due to damage of the immediate area sufficiently different from the disruption of oxygenated blood to the brain from a heart attack sufficient within your system to classify one as 'oxygen starvation'...but not the other?

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OK I am stopping here because you don't seem to be comfortable when someone uses a LOT of words.

(edit: a little late for stopping early....oops)

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Well, there you go again.

Eschew Obfuscation!

Espouse Elucidation!

Anyway, you aren't using that correctly.

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Just because your don't have the means to pay attention through a particular comment, does not mean the comment is beyond comprehension. It just means you'll have to ask someone who can afford to pay attention.

"When there is insufficient O2, cells do not just call it quits and throw in the towel. Luck for us they switch to anaerobic metabolism." ???

I don't know where you get your half-baked physiology from, but you should know that brain cells are incapable of anaerobic metabolism. Period. The rest of your ramble is equally uninformed. As for your trumpeting that "life does not end right when the O2 runs out." you should understand that death is not an instantaneous event, but a process of shutting down. It is still the oxygen failure that triggers the process.

'''.I don't know where you get your half-baked physiology from, but you should know that brain cells are incapable of anaerobic metabolism....."

Curious.

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. Anaerobically, the brain switches to the significantly less efficient glycolytic pathway for its most basic energy requirements. Anaerobic glycolysis provides the adult brain with a limited amount of energy and time to maintain ion homoeostasis and other essential processes before several events occur that lead to brain cell damage and death

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and

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For the next four to six minutes, brain cells continue to burn some remaining reserves of glucose in the absence of oxygen. This can be compared with a flame on a gas stove which burns blue when oxygen is mixed with the gas but turns yellow, creating waste byproducts, if oxygen is insufficient. In brain cells, the transition from aerobic (oxygen-based) metabolism to anaerobic (oxygen free) metabolism creates byproducts including lactic acid. Acidity also increases as carbon dioxide (which is no longer being removed by the blood stream) dissolves in water to form carbonic acid. The increase in acidity alone has harmful consequences, but other processes also begin to disrupt the extremely complex chemistry of brain cells, jeopardizing their survival.Cells normally use a large part of their energy to maintain a higher concentration of potassium salts and a lower concentration of sodium salts inside their membranes than outside them. When a cell runs out of energy, it cannot sustain these chemical differentials. Potassium leaves the cell and sodium enters, together with water, which causes cells to swell.The imbalance of sodium and potassium results in the release of glutamate (glutamic acid), which is a neurotransmitter. This in turn triggers receptors which allow calcium ions to enter the cell, provoking a further release of glutamate in a positive-feedback loop. High levels of calcium eventually activate proteolytic enzymes that destroy many cell proteins (especially in cell membranes) and initiate apoptosis, causing cells literally to self-destruct 2.

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I have no problem providing reliable references to support what I wrote.

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Turn about is fair play. Care to divulge where you dig up your half baked ideas on physiology?

Actually, I have a BSc in physiology and wrote a thesis on the respiratory centres. My subsequent professional career was based on supporting the oxygen requirements of seriously ill patients. Anaerobic metabolism in brain cells is a precursor of brain cell death: Robertson et al
The predictive value of cerebral anaerobic metabolism with cerebral infarction after head injury.
Journal of Neurosurgery September 1987 / Vol. 67 / No. 3 / Pages 361-368

The cause of death in the OP's posted scenario is the lack of oxygen available to the brain cells.

'...Actually, I have a BSc in physiology.....'

...with a minor in duplicity, apparently.

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This is from your post previous to the last:

'....you should know that brain cells are incapable of anaerobic metabolism. Period.....'

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This is from your last post:

'...Anaerobic metabolism in brain cells is a precursor of brain cell death: _{Robertson et al}

The predictive value of cerebral anaerobic metabolism with cerebral infarction after head injury.

_{Journal of Neurosurgery September 1987 / Vol. 67 / No. 3 / Pages 361-368}...'

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You didn't feel even the least bit weird about using that quote to support you previous attack; even though it materially contradicts what you stated in your previous attack?

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I haven't yet reviewed the article you sight (in part because you provided no link), but all appearances suggest, without obvious ambiguity, that the article you sighted probably does an excellent job of supporting my point.

"with a minor in duplicity, apparently.

Thank you for that.
Brain cells are as incapable of anaerobic metabolism as you are of flying off a cliff by waving your arms. You attempt it - you die shortly afterwards.

Of course, you could always surprise the world and provide evidence to the contrary.

'...Brain cells are as incapable of anaerobic metabolism as you are of flying off a cliff by waving your arms....'

Yeah, no one would want to do that. That doesn't sound like any fun at all. Certain death.

You are not flying and the brain cell is not in controlled survival.

In any case, it is neither myself nor the rest of the forum who you have to convince; it is the entire medical profession. You therefore have a choice:

1. Write up your insights into the survival of the anoxic brain cell in a reputable journal.

2. carry on trolling

Which is it to be?

Plurium Interrogationum is the name of the fallacy you are attempting to foist upon the discussion (further evidence I may have guessed correctly about your minor).

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I suspect it is an effort to draw attention away from the severe contradictions I pointed out in your previous comments (and in such close proximity!).

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I'll explain once again why your explanation fails. I'll be brief.

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If your argument relies on disallowing, as proximate or ultimate, other causes of death that trigger oxygen deprivation to the brain;

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and it has been established that brain cells continue to metabolize for a short time in the absence of oxygen, and that ultimately cells perish from things like sodium ions rapidly entering the cell and the destruction of the cell wall and destruction mitochondria;

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then it is grossly inconsistent to claim oxygen deprivation is the proximate or ultimate cause of death, because it triggers the eventual demise (since you were unwilling to consider causes of death that trigger the ultimate demise and have oxygen deprivation as part of the chain).

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It is ridiculous to disqualify all prospective candidates with a certain trait, except the candidate with the same trait that happens to be your favorite. If you insist on no triggers, it has to hold for lack of oxygen as well.

Thank you for clearing that up...

Bicycle sprinters use their muscle cells anaerobic ability to go full out for short periods of time. It's a well known and much employed physiological fact.

That is true, and many other tissues besides muscle are capable of anaerobic metabolism. However, brain cells are not capable of doing so and surviving. It is the brain cell at the centre of this discussion.

OK, clear up one more thing for me. I fully understand that brain cells will start dying off well before other tissues but...

If brain cells cannot survive once they go into a state of anaerobic metabolism and it only takes 6 minutes for that to happen how would you explain how it is that people who fall through the ice can be under water for as long as 20 minutes and then be revived with no brain damage?

Athletes like record breaking free divers have recently broken the record by holding their breath for over 20 minutes!

http://www.dailymail.co.uk/news/article-2154442/Free-diver-breaks-world-record-holding-breath-underwater-22-22-minutes.html (Note that they usually have a 20% larger lung capacity than 'normal' people.)

When I was competing in AAU swimming competition I was able to kick a full 100 yards or more underwater with no problem, repetitively. That is a lot different than just holding your breath which at the time I could easily do for 4 minutes.

I transfered to IU Bloomington and stopped swimming competitively when I realized I'd never place first again since Mark Spitz was on the team and we would both be swimming the same events. Better to spend my time in the biochemistry lab and the library. :)

Gentlemen,

After reading the replies to my question I have noticed a fairly wide variation in what is considered too little O2 or too much CO2.

But it was reported that athletes will voluntarily breath air with O2 concentrations as low as 12%. Yet it was also reported that 12% produced loss of consciousness.

It was reported that concentrations of CO2 as high as 5% were used medically to encourage deep breathing and 7% produced loss of consciousness.

It was also reported that there was some variation on these effects between individuals.

Based on the above perhaps we could say that the lowest tolerated O2 level is 12% and the highest CO2 level is 7%, keeping in mind that these are rough figures and there is some variation.

Since O2 becomes CO2 simply by the addition of a carbon atom it might be true that for every O2 used by a person, a CO2 is produced. So for every 1% of O2 decrease there is a 1% increase in CO2.

Since the O2 starts at 21% and the CO2 at 0%, a decrease in concentration of O2 to 12% would mean a 9% increase in CO2 to a concentration of 9%, well above the loss of consciousnesses level of 7%.

On the other hand, an increase of CO2 to 7% concentration, the loss of consciousnesses level, would only require a drop in O2 concentration of 7% down to 14% about halfway between "not noticeable" at 17% to "tolerated by athletes" at 12%.

From the above, it would seem our trapped victim would loose consciousnesses, in distress, from the effects of elevated CO2 before the effects of lowered O2 levels would make him simply fall asleep.

I don't have the data to shed any light whether death would be caused in the same way as loss of consciousnesses.

bandership

Welcome to the wonderful world of statistics in relation to biological measurement. In an ideal physics-based world, the oxygen concentration above which survival is guaranteed and the oxygen concentration below which death is assured would be one and the same number, but biology is not like that. Each oxygen concentration has to be related to a probability of survival of individuals in a population. The figures are complicated by the population studied. If you take a helicopter from sea level to 5000m you will become acutely breathless and very unwell, yet Andean Indians live their lives at those altitudes. It is therefore not appropriate to extrapolate from the trained athlete's capabilities to those of the general population, and it is not surprising that so many different numbers appear in relation to different aspects.

There exists the possibility that the XY genetic complement has overrun the forum and the XX has been ignored. See the above address.

A wise man told me: "You always pass out before you die" - (Basketball coach's comment as we were running laps around the gym in agony) CO2 will make you lose consciousness from acidosis, lack of O2 shuts down cellular respiration, CO blocks O2 uptake into your blood. Your body monitors CO2 and pH from blood concentrations. pO2 levels drop during drowning or suffocation and you pass out before your brain and body shut down. Coach was right.

They died in that 'small air-tight place' because they turned a sufficient amount of oxygen into carbon dioxide to change the relative (life sustaining) percentages of both compounds creating an atmosphere that would no longer sustain mammalian life.