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Message: <blockquote data-quote="MaxKaladin" data-source="post: 1604663" data-attributes="member: 1196">Well, one thing to remember about SCUBA diving is that it pretty much just involves "standard" air at increased pressures.  It won't be much use dealing with different atmospheric compositions and won't predict all of the problems with lower than normal pressures.  That said, I think your biggest problem will be atmosphere composition.  Air with less than about 16% (IIRC) oxygen is not survivable for most humans.  Then there's all the other stuff that might be in the air.  Some of it might be quite harmful to humans.  Issues of pressure take a back seat to atmospheric composition.  With all the volcanism you mention on the one planet, I'd imagine that atmosphere is unbreathable.  At the one extreme, you have a Mars with 0.5 ATM of pressure.  That's still more than at the top of Everest, so its survivable but non-natives used to a 1ATM environment will probably require occasional use of supplimental oxygen like high altitude climbers and would get winded very easily.  They might have to worry about the bends if they spend long times at this pressure and then suddenly try to transfer to a normal pressure (Climbers descend too slowly for this to be a problem -- its rapid change that does it).The other extreme, 3 ATM is about the pressure divers experience at about 100 feet underwater.  A diver can only stay at this depth for a few minutes before needing to return to the surface.  If they don't, they risk the bends.  Even if they start to return, divers are expected to make decompression stops to give their bodies time to gradually get rid of the compressed nitrogen bubbles in their systems before they become dangerous.  Even with all of this, exposure should be limited to a short time to avoid problems, which means that repeated trips in a day are pretty much out.   I'd imagine your 3 ATM planet would probably not have non-natives moving around without some sort of rigid shell suit that would protect against the atmosphere.  Its probably a moot point since the atmosphere would almost certainly be unbreathabe with all that volcanic activity going on. Nativse of this planet in a standard atmosphere would be about like humans at the top of Mount Everest.  There would be a need for supplimental oxygen at the least and they would become tired easily, assuming they could breath the air at all.  The middle ground is at 1.3 ATM.  My rough guess would be that people could move around for moderate periods of time here.  A good rule of thumb in diving is that 33 feet (10.1 Meters) of water depth is equal to an additional 1 ATM of pressure, so 1.3 ATM is about like being at the bottom of a swimming pool.  Its been years since I read the charts, but I think you can expect to be able to use air at that depth for over an hour without expecting any real problems, so I'd expect that people in a 1.3 ATM enviroment could probably do about the same.  Without the compressed air problem, you would probably just need to worry about moving suddenly from high to low pressures .  Disclaimer:  I learned SCUBA diving more than ten years ago and got a certification, but I'm really rusty on all the exact numbers and possibly on some of the theory -- especially if its relatively recent -- so all of this should go with a grain of salt.Edited to correct myself.</blockquote>

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