What kind of atmospheric composition and density is required for humans to be healthy while gaining oxygen and removing carbon dioxide through their lungs without expanding and contracting their lungs with their diaphragm, instead only by keeping their throat open for passive diffusion of air in a manner similar to insects?
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12$\begingroup$ While I do not know enough to say definitively, I highly suspect that the answer is, "It's impossible." $\endgroup$– In Hoc SignoCommented Oct 30 at 19:19
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2$\begingroup$ Welcome Alexander, please take our tour and refer to the help center. Please bear in mind that oxygen concentrations much above Earth's are toxic to humans. See this previous question: What is the highest concentration of oxygen a human being can reasonably survive?. You can use the search facility at the top of the page at any time to get what we've previously covered. $\endgroup$– Escaped dental patient.Commented Oct 30 at 19:38
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3$\begingroup$ It's not the air that prevents this it's our size. $\endgroup$– PelinoreCommented Oct 30 at 22:03
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2$\begingroup$ Just to be clear, are you asking what the nature of the atmosphere must be for an average adult male or female human as we understand them today to absorb oxygen and discard carbon dioxide without the use of lung muscles to force the air in and out through the esophagus? (That last clause should give you a lot of pause. The surface area of the lungs isn't the problem.) $\endgroup$– JBHCommented Oct 31 at 0:44
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$\begingroup$ Name it non-contact mechanical (pressure) ventilation and handwave a cause for how it works ;) basically a big subwoofer $\endgroup$– DonQuiKongCommented Nov 1 at 13:01
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2 Answers
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The Air would become caustic and burn your skin first
The rate of diffusion for oxygen in air at room temperatures is no more than 0.0000198 m2/s. It might actually be much lower because of the high moisture content in your lungs. Oxygen diffuses about 1000 times slower through water than in air; so, moist enviornments can have a major impact on O2 diffusion. The trachea has a cross-section of about 0.00025m2 and breathing typically causes a 5% reduction in O2 which according to Fick's law tells us that diffusion can only take care of about 2.475e-10 m3/s of O2 transfer. Humans breathe an average of 20m3/day of air which translates to 2.31e-4 m3/s. In other words, it would take just shy of 1 million times as much atmospheric O2 for people to be able to breath passively just by holding their mouth open.
The reason bugs can do this is because like us, they do have an active breathing system, it just does not include lungs, but rather an expanding and contracting of their exoskeleton.
All this said, air starting at about 5-7 times as much total oxygen as the Earth's atmosphere will become caustic: slowly dissolving your skin and eventually killing you; so, the human body can not get anywhere close to being able to survive this way.
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This works only for few-cellular organisms where every cell can reach the surroundings. Those live in solutions, though.
Air breathing animals breathe actively.
- Mammals, reptiles and such have lungs, ellastic case (ribs) and diaphragm to drag air in and out their lungs.
- Birds have fixed ribs, but their lungs extend to their bones, so every move drags air in and out through their lungs
- Insects have vents in their exoskeleton and pump air in and out through those vents.
if you watch a wasp or bee closely you can see their buts are quite simillar to a telescopic antena and they pump their buts in and out to breathe.
If you want to keep the lungs (or whatever organ responsible for air-blood gas transfer) not deforming, you need to flow the air through - like fish with water and their finns.
It is much easier to pump air in and out of a cavern, than force it to flow though something.
How hard is it to build turbine compressor and how hard is it to build piston/diaphragm compressor? What are their opperation ranges (air flow, working pressures) and such?
