Wow, very interesting. I had a pre-conceived notion that Martian atmospheric pressure was something like 20% of ours, but you're right, it's quite a bit lower than even that.
If it was 20% that would be survivable with just an oxygen mask fwiw. Humans can go down to 16% atm pressure safely if they breathe 100% oxygen. The rest of the body can easily handle the pressure difference (1 full atm of pressure is equivalent to being 10meters underwater as a guide, human orifices have no issue with it contrary to pop sci beliefs).
So yes it's not 20% and it would be nice if it was.
As in if you go 10meters underwater your orifices experience 1atm of pressure difference. In the reverse to space but the point being you can handle this just fine.
There's a myth that at low atm of pressures you pop and such. This is not true. You may need to breathe in/out to adjust but pretty much every part of the body can handle 1atm of pressure difference just fine. The 10meters below was intended as a reverse example but the point holds.
Except with pressure changes, physiology absolutely changes. There is some room for error within small changes..but at extremes its definitely different. (and Mars is 100% an extreme)
Its why in SCUBA you have to calculate MOD for nitrox. Because the partial pressures of oxygen will kill you. We only breath about 21% oxygen in air. And after rec depths, you often using different mixtures and take on decompression obligations, trimix, heliox etc. At certain pressures, things like HPNS will also have an effect.
You definately cant survive in a vacuum either with just a mask. Its why pressure suits are a thing.
