Cybersuit -- Submersible or Not?

[vicky_molokh]

Originally Posted by Ransom

I think the reason this doesn't fit our sense of reality is we are overestimating the forces involved in 30 atm of pressure and underestimating the forces involved in blunt trauma damage. A punch powerful enough to deal more than 5 points of damage is going to be putting out a lot more force than 30 atm.

Sources: Google tells me that 30 atm is in the ballpark of 440 psi, and that the average heavyweight boxer's punch (which by gurps rules should sometimes but not always deal damage vs 40 flexible DR) inflicts a force of 1200 to 1700 psi. So even armor that doesn't protect from moderate punches should still be more than enough to resist 30 atm of ambient pressure.

Originally Posted by Ulzgoroth

Those 440 psi are over a whole lot more than 4 times the area. In terms of total forces, the punch doesn't come close.

How does one ever have "440 psi" over "a whole lot more than 4 times the area"? PSI is already measured across a unit of area. So 440 PSI over an area of 4 square inches would be the same 440 PSI.

[vicky_molokh]

Originally Posted by Ransom

I think what Ulzgoroth is saying is that 440 PSI * [surface area of suit] > 1600 PSI * [contact area of punch], and suggesting that this implies that the air pressure would require more rigidity to resist than the punch. I'm not sure I agree since it seems to me that the force per area would match damage more closely than the absolute force, but I don't know enough about physics to be sure.

But the point of pressure resistance is that it isn't the same thing as resisting a highly asymmetric application of force like a punch. Again, squishing an egg in one's hand is significantly easier if one applies pressure unevenly (e.g. using a couple of fingers) than if one tries to do it deliberately very uniformly with two hands.

[Bira]

I think it's quite possible that the cybersuit does something like flood the user's lungs with breathable fluids and other such adjustments. It is a TL 11 item after all, so it can probably take those techniques far enough for them to be good at 30 atm without needing to be rigid.

[Ulzgoroth]

Yes, I'm not saying that the pressure has higher penetration, insofar as that's even halfway meaningful. But when you put things in terms of force, well, there's a whole lot of it involved (unless you do the vector sum, in which case there's almost none).

However, the point about huge force totals does have importance. Supporting that pressure over, for instance, the pressure hull of a submarine takes impressively sturdy construction. And in the case of a thin suit, you not only have to hold out the pressure in a much less structurally sound shape, you have to do it with almost no deformation, because there isn't room to deform while keeping the pressure off the occupant.

Originally Posted by Bira

I think it's quite possible that the cybersuit does something like flood the user's lungs with breathable fluids and other such adjustments. It is a TL 11 item after all, so it can probably take those techniques far enough for them to be good at 30 atm without needing to be rigid.

That doesn't provide Pressure Support, though. Humans can survive for a bit at significantly increased pressures, but long-term our physiology doesn't hold up. (And if it did, we'd already have Pressure Support, it wouldn't be the suit providing it.) If armor provides Pressure Support, it means you can have the inside at a much lower pressure than the outside.

[Flyndaran]

Originally Posted by Bira

I think it's quite possible that the cybersuit does something like flood the user's lungs with breathable fluids and other such adjustments. It is a TL 11 item after all, so it can probably take those techniques far enough for them to be good at 30 atm without needing to be rigid.

Breathing liquid is insanely exhausting and of course prone to all sorts of risks gasses don't have. I believe it's also horribly unpleasant what with all those instinctive feelings of drowning as it's first going in.
I'd imagine ultra tech gear is LESS likely to psychologically traumatize its users, but that's just my opinion.

[Flyndaran]

Originally Posted by Ulzgoroth

...
That doesn't provide Pressure Support, though. Humans can survive for a bit at significantly increased pressures, but long-term our physiology doesn't hold up. (And if it did, we'd already have Pressure Support, it wouldn't be the suit providing it.) If armor provides Pressure Support, it means you can have the inside at a much lower pressure than the outside.

For humans taken slowly down, risks come first and foremost from dangerous gas mixtures and specific toxic effects from them rather than pressure.
Oxygen becomes toxic long term above around 0.4 atm partial pressure which would be air at just twice sea level. Keeping that at safe levels requires other filler gases which themselves become toxic at high pressures. Nitrogen narcosis, high pressure nervous syndrome for helium, etc.

Pressure support is most useful for going up and down quickly, something that kills people that when done slowly is almost trivial.

[vicky_molokh]

Originally Posted by Nereidalbel

That's their native pressure, and for many of them, coming up to the surface is a good way to end up dead. For life evolved on Mars, humans would be the ones with Pressure Support.

Okay, I don't know which fishies have a big variation of acceptable pressure, so I'll get back to mammals:
Sperm whales. Diving up to 3,000 yards underwater, which is almost 300 atmospheres of pressure. That's Pressure Tolerance 3 right there. But I think at most they'd qualify for DR (Tough Skin), not for something rigid.

[Ulzgoroth]

Originally Posted by vicky_molokh

Okay, I don't know which fishies have a big variation of acceptable pressure, so I'll get back to mammals:
Sperm whales. Diving up to 3,000 yards underwater, which is almost 300 atmospheres of pressure. That's Pressure Tolerance 3 right there. But I think at most they'd qualify for DR (Tough Skin), not for something rigid.

But if you put a human inside a sperm whale and run them through that, they'll die horribly.

A creature having large pressure tolerance range usually (probably always for non-fictional organisms) means having physiological adaptations to cope with various pressures and changing pressure, not actually resisting the pressure in any way. A suit of armor or vehicle providing pressure tolerance means that it actually sustains a pressure differential, allowing the occupant to remain at a tolerable pressure while the outside environment does not.

[vicky_molokh]

Hmm. Checking the information on hard-hat diving suits (of leather or airtight cloth, despite a hard helmet), reportedly they can be used down to a depth of 180 metres, which is 18.8 atmospheres, which in GURPSese would indicate slightly above Pressure Support 1 (which grants ability to function at 10 atmospheres).

[sir_pudding]

The purpose of drysuits is thermal insulation, not pressure support.