In my short story, an astronaut is in Earth orbit doing a spacewalk in your standard variety spacesuit and is just about to enter airlock back into the ship. However, just as the airlock door finished opening a disaster strikes. A piece of small debris hits the glass portion of the helmet shattering it.

Fortunately, the trajectory was such that the glass portion of the helmet is the only thing hit. Somehow the resulting glass shards do not do any damage to the person (Perhaps the pressure of the suit caused them to mostly fly outwards rather than towards the face). The only effect on our protagonist is the head being suddenly and immediately subjected to the near-vacuum of low Earth orbit. This is not a death sentence as the airlock is right there. After a very brief stun, the astronaut enters the airlock and hits the door close & automated pressurization control before passing out from the lack of air. Once pressurized, other crew inside open the internal airlock door and provide assistance. The protagonist survives and the story continues.

It is well known that human skin will be perfectly fine withstanding this ordeal. What I am not sure about is the condition of the eyes. While it is a reflex to immediately shut one's eyes in danger, in my story the person never does during the whole ordeal. The surface of the eye is subjected to near-vacuum the whole time.

The moisture of the eye will boil off immediately, but will the surface of the eye rupture from the sudden drop in pressure? Just how durable are the surfaces of our sight organs? Will my protagonist is now blind for the rest of the story?

Will the sudden pressure drop from 4.3 psi (Pressure of the suit) to zero be violent enough to dislodge the eyeball out of the socket?

Regardless of the level of the immediate damage, is the protagonist able to keep their ability of sight or must they find the close/pressurize switch by touch?

Thank you for reading.

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    $\begingroup$ Possible duplicate or at least related to worldbuilding.stackexchange.com/questions/138712/… $\endgroup$ Dec 21, 2021 at 2:59
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    $\begingroup$ The "glass" portion of the helmet is made of a polycarbonate. It doesn't shatter. (It is incapable of shattering. A projectile may pierce a hole in it, but it cannot break it into shards. It is very similar to the material of which bulletproof windows are made.) (Technically, it is indeed a glass, that is, an amorphous solid which exhibits a glass transition, but it is an organic glass, not silica glass.) $\endgroup$
    – AlexP
    Dec 21, 2021 at 4:44
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    $\begingroup$ @AlexP Try to hold your breath against vacuum decompression and you're asking for a lung rupture, just as if you'd held your breath when ascending ten meters from a SCUBA dive. $\endgroup$
    – Zeiss Ikon
    Dec 21, 2021 at 16:35
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    $\begingroup$ @AdrianColomitchi Oxygen via mask without pressure support on the chest will simply result in the lungs inflating to their elastic limit. The decompression victim will be unable to exhale; most humans (other than circus strongmen who demonstrate blowing up hot water bottles) can only produce around 0.07 to 0.15 bar by exhaling. This is below the level that can sustain life, so you've either got too little oxygen to live, or you're in danger of ruptured alveoli. $\endgroup$
    – Zeiss Ikon
    Dec 21, 2021 at 16:38
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    $\begingroup$ Pure oxygen at .25 bar is enough to stay conscious, and might not be enough to cause wholesale alveoli ruptures (though it's above the safety limit for SCUBA ascent) -- but it's too much to exhale against if you have no other pressure support on your chest and abdomen. $\endgroup$
    – Zeiss Ikon
    Dec 22, 2021 at 14:14

1 Answer 1


Such accidents have occurred, where a human has been exposed to a near vacuum, below the Armstrong Limit pressure, and have survived, by being recompressed before permanent injury or death have occurred.

See Effects of Spaceflight on Wikipedia: NASA engineer Jim LeBlanc was exposed to a near vacuum in which the saliva boiled on his tongue, and survived with only an earache as the noticeable ill effects.

It can be assumed that since unconsciousness will occur rapidly on exposure to vacuum, and the eyes close when unconsciousness occurs, that the eyes are effectively self-protecting, even if not consciously closed. A person exposed to vacuum wouldn't be able to remain conscious and active long enough for any significant damage to occur to the eyes assuming that they survive the experience.

I'd be more worried about ear trauma resulting in deafness.

I would expect that the victim's eyes would remain functional - to a degree - until they lose consciousness. The sudden pressure change may result in blurred vision, but tasks requiring no great visual acuity - such as hitting a reasonably large switch - ought to be possible.

  • $\begingroup$ Will the person be able to see throughout this 15 second ordeal before passing out? Can they see the switch or need to hit it by touch? $\endgroup$
    – Lotana
    Dec 21, 2021 at 21:29
  • $\begingroup$ @Lotana I would expect so. See my edit. $\endgroup$
    – Monty Wild
    Dec 22, 2021 at 14:02

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