Are you sure about that? If we drop a full 80 cuft tank to 2 ata, the tank will only have 40 cuft of air at that depth? Interesting.
air consumption versus depth
- Thread starter cogitoergo
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Are you sure about that? If we drop a full 80 cuft tank to 2 ata, the tank will only have 40 cuft of air at that depth? Interesting.
JeffG
Contributor
The Tanks air volume doesn't change. Its a pressurized vessel. (Like a Sub).
The Air volume changes when it is released into the 1st stage.
having fun.
JeffG
Contributor
I know. I just quoted everthing just so that someone who doesn't know physics could take the statement in context.
Jeff
cogitoergo once bubbled...
I'm new to scuba diving. One of the first teachings that went against my intuition and physics background was the increased air consumption as depth, and breathed air pressure, increase. There is a lot of material out there that relates this phenomenon to the fact that a breathful of air at 2 atm - for instance - will in fact contain 2 breathfuls of surface air. At that rate, the tank will deplete twice as fast. What I don't get is that in that same breathful of 2 atm air, there is also twice as much oxygen. And if there is more oxygen, we should be able to take fewer breaths. After all, the amount of O2 in the tank is the same at any depth. Why is that same amount of O2 not allowing me to produce the same work at 2 atm as it would at 1? One final note: If I go to a Colorado ski resort, where the atmospheric pressure is far less than 1 atm, I will take many more breaths of the same volume as I would at sea level for the same work output. Why isn't the reverse also true when I go diving at depth? Are we so limited in the rate of oxygen we can process? Are we breathing out - and wasting - more oxygen at depth?
Hey cogitoergo: you mentioned you have a physics background and so do I... but most of this stuff is chemistry (gas laws) and biology (the voodoo of physiology).
Anyway... I can sort out your questions and try to give you some idea of what to search for out on the web but frankly, space and time are limited here!
By the way... many have already explained to you what triggers the breathing reflex... little hoohoos reading co2 levels in the blood... actually I think it's blood pH that's read by these receptors but whatever... the level of oxygen has nothing to do with it.
More importantly and in answer to your original question, the body's ability to metabolize oxygen is a constant... or at least has a maximum potential... termed V02Max... and this varies from individual to individual. It has to do somewhat with genetics and somewhat with how well practiced your body is at using oxygen. You probably know about hemoglobin (or as my yougest daughter once called this chunky little protein: Homo-goblins), and red-blood cells. Well, these little buggers work to rule as it were and once they max out, giving them more oxygen really doesn't make any difference to how fast or how efficiently they work.
Oxygen uptake is measured in millilitres of oxygen used per minute per kilo of body mass. Uptake of your average diver in poor condition might be 20ml/kg/min while a well conditioned athlete might be 75 or higher! Diving and what happens to the gas you breath does not mean your body's VO2Max increases in direct relationship to whatever is happening to the gas.
HEY, BUT WHAT IS HAPPENING TO THE GAS?
First, changes in ambient pressure do not effect the fraction of oxygen in a given mix... if we are talking air, then the fraction of oxygen at sea level and at 100 feet (or up in a snow field at 18,000 feet) is the same -- well to all intents and purposes.
However, the partial pressure of oxygen will change. At sea level it's about 0.21 ATA, at 18,000 feet it's about 0.11 ATA -- and unless we are aclimatized to it, will mean we faint and pass on to the great double black diamond in the sky -- and at 100 feet breathing from a scuba tank, it's about 0.84 ATA.
WHY? Well you already know, the air we breath in the mountains is less dense than the air we breath at sea level, and the air we breath at 100 feet has to be four times as dense as that to overcome the pressure down there and fill our lungs. Hence, that 80 cubic foot tank of compressed air at 100 feet will still contain 80 cubic feet of air, but we'll use it about four times as fast as on the surface. Sure, out bodies are "getting more oxygen" -- and we express that by the increase in partial pressure -- but our ability to do anything useful with it is limited by our physical conditioning... and that has nothing to do with physics... it has to do with 30 minutes of arobic exercise at least 3 times per week!
Doppler
Bob C
Guest
Thanks Doppler. You seem to be the only one that addressed cogitoergo's queston. I'm just an engineer, but it helped me understand it better also.
Bob C.
Bob C.
Laser
Guest
The simple answer is always the best.
OP
cogitoergo
Guest
Indeed. But the question is not how much we fill our lungs. The question is whether when we fill our lungs fully with 2 or 4 times the pressure - and therefore 2 or 4 times the number of O2 molecules - we can produce 2 or 4 time more work, or alternatively we can breathe 2 or 4 times slower.
The answer seems to be no. That no matter how many of these O2 molecules are bouncing around in our full lungs, we can only use a small amount. And that even though we have more than enough O2 in there, we still want to get more in because our body doesn't know we have enough. It apparently knows how much CO2 it needs to get rid of.
It would be interesting to know if in a re-circulating breathing system, the diving times are affected by depth.
Thanks to all of you for the very informative comments.
chrpai
Contributor
Yes, but because of No Decompression limits not by air supply. ( Except that amount of air used to equalize the loop on the descent and compensate for suit squeeze is greater the deeper you go. )
ScubaJorgen
Contributor
Apparently the amount of hemoglobin or the transport of the hemoglobin is the limiting factor in o2 uptake. This makes sense: sporters often train a period in the mountains. The body responds by making more of the hemo stuff. When going back to sea level the sporter performs better :lifter: because he is able to supply his muscles with more oxigen (a more lousy sporter would just get drugged to have the same effect :HAHAHA: :shame: ).
Would be interesting to put a diver in the mountains for a while. Having more hemoglobin would mean the diver is able to extract more o2 from a breath before the co2 level forces him to exhail :errrr: . However, he somehow has to do something with the o2. Doplers excercize
Would be interesting to put a diver in the mountains for a while. Having more hemoglobin would mean the diver is able to extract more o2 from a breath before the co2 level forces him to exhail :errrr: . However, he somehow has to do something with the o2. Doplers excercize
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