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I was reading the question asked here in regards the Alexander Gerst's patching of a small (5mm) hole with his thumb temporarily. This got me wondering, if his thumb was only fine because the majority of it was part of the ISS atmosphere, at what point would it not be okay to do this?

Two main scenarios come to mind that have me intrigued:

Ignoring that the hull is likely too thick to support either of these scenarios...

If the hole were the size of his finger-tip and he plugged it such that the entirety of his finger-tip was through the hole, would the results be different? Would his finger tip sustain more damage?

What about simply sticking your thumb through a hole that was created for a thumb to be stuck through it, with a perfect seal between the interior and the exterior of the ISS?

Alternatively, more simply put, where would the damage stop? At the hull interior?

Is the thickness of the hull the only thing that saved him from damage-- the fact that he wasn't actually "outside" of the ISS "atmosphere" at any point?

Looking for the limitations in this question. What would happen over the course of:

  • 5 minutes?
  • 1 hour?
  • 10 days?
  • As much time as it needed to fuse you to the hull?
  • Where would it stop, would it?
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    $\begingroup$ Space vacuum isn't any worse than a decent vacuum on earth. Supported skin is vacuum proof for at least a while. Unsupported skin starts bruising pretty fast and broken blood vessels happen if the area exposed is large. A thumb exposed to vacuum would swell and start to take damage, but a few minutes probably wouldn't do anything that wouldn't heal. $\endgroup$
    – zeta-band
    Commented Sep 4, 2018 at 21:08
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    $\begingroup$ Reminds me of the old Robert Heinlein story "Gentlemen, Be Seated" where a leak is patched temporarily with a...different....anatomical part. $\endgroup$ Commented Sep 4, 2018 at 21:09
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    $\begingroup$ @MagicOctopusUrn It's a old story, probably from the 40s, and only mildly ribald. $\endgroup$ Commented Sep 4, 2018 at 21:15
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    $\begingroup$ What I imagine your first suspicion was, was addressed in the Shuttle inflight maintenance checklist (sadly not online) for the case of setting up a urinal which exhausted directly to vacuum. It included the immortal line "WARNING - DO NOT HARD DOCK" $\endgroup$ Commented Sep 4, 2018 at 21:18
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    $\begingroup$ I imagine sticking your thumb/finger through a hole might be problematic once the finger swells… you may not be able to retract it. $\endgroup$
    – DarkDust
    Commented Sep 5, 2018 at 9:06

1 Answer 1

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This type of injury is referred to as “Barotrauma” https://en.wikipedia.org/wiki/Barotrauma . The bruising is caused by rupture of capillaries and small veins. Normal capillary pressure is 0.19-0.44 psi above ambient, but this becomes 30x higher when a body part is exposed to hard vacuum. This results in rupture of capillaries (a Hickie) but also leakage of plasma from the intravascular space into the extravascular space. Swelling, in other words.

The situation is even worse in venules (small veins ) because they are larger in diameter than capillaries, so higher wall stress is developed.

The specific situation you describe, where a finger is poked through a sealed hole between the 14psi ISS and hard vacuum, is very bad news. The swelling would rapidly cut off arterial blood flow (2.32 psi) to the finger. The finger dies, turns black and falls off a few weeks later. This is called Ring Tourniquet Syndrome when caused by jewelry rings https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6581218

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The amount of permanent injury depends on the duration of interrupted blood flow (called ischemia) and the temperature of the ischemic body part. One series https://pubmed.ncbi.nlm.nih.gov/20179474 reviewed 25 fingers which had been severed and surgically re-implanted more than 24 hours later. They had a 64% “success” rate. “Success” meant the reimplanted fingers stayed pink instead of falling off. They didn’t necessarily work very well. Stiff, non-functional fingers are a big enough nuisance that patients sometimes request to have them amputated.

So, to answer your questions:

  • If the hole was the diameter of his finger tip, more damage would have resulted.

  • If you stuck an entire finger through a hole, the finger would be
    damaged up to the hull line. After a few minutes, the finger would
    swell to the point where it could not be retrieved. The only
    realistic action would be to cut the finger off flush with the hull. Then put a patch on the hole... which is what should have been done in the first place. A finger-sized hole in the ISS is a pretty relaxed emergency. There is plenty of time to reach for the patch kit.

The severed finger would likely shoot out of the hole into space (like a pop-gun) due to the 14psi atmosphere in the ISS. Orbital mechanics would return it to the ISS one orbit later. So, if you could arrange an emergency EVA with a catcher's mitt, the finger could be retrieved.

Note: the Little Dutch Boy got away with his antics because the pressure in the hole was positive, not a vacuum.

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