What happens to a person's body in space without a spacesuit?

[Pelf41]

If pressure in a vacuum is very low, water can evaporate even at low temperatures, since the lower the pressure, the lower the boiling point.
So, if I were suddenly exposed to the vacuum of space, would my body freeze, or would it expand as the water in my body turned into gas?

 

[kuruman]

See https://www.thoughtco.com/human-body-in-a-space-vacuum-3071106 for example.

 

[Baluncore]

So, if I were suddenly exposed to the vacuum of space, would my body freeze, or would it expand as the water in my body turned into gas?

Uncontrollable burps and farts: Embarrassing.
Internal gas embolism and colic: Painful.
Accelerated desiccation and freeze drying: Preserving.

 

[DaveC426913]

Something to consider is that your skin is not merely a bowl of water. It acts as a partial barrier to vapourization of water (mucosal membranes notwithstanding). Not a complete barrier, but sufficiently so that a number of other things - relating both to low pressure and extreme cold - will harm you in the meantime.

 

[Baluncore]

Something to consider is that your skin is not merely a bowl of water.

With age, the skin becomes wrinkled. Space works faster than Botox.
May I introduce you to Monsieur Bibendum, the Michelin man.

 

[DaveE]

Clearly not a scuba diver asking.

Even though space is cold, it's also a pretty good insulator. Heat transfer is from radiation and happens more slowly than anything related to pressure changes.

 

[OmCheeto]

Clearly not a scuba diver asking.

Even though space is cold, it's also a pretty good insulator. Heat transfer is from radiation and happens more slowly than anything related to pressure changes.

Interesting thought. If someone were to exit the ISS with only a scuba tank for air, and maybe a mask to keep their eyes from drying out, how long would they then survive?

General googling says the irradiance at the ISS is ≈1360 watts/m² and this site says a 1m² black body @ 90°F emmits ≈500 watts. This mean the person would actually warm up!

We should probably give them a water bottle as it seems to me their body might try and sweat all that extra energy away.

 

[A.T.]

Heat transfer is from radiation and happens more slowly than anything related to pressure changes.

What about sweat evaporation?

We should probably give them a water bottle as it seems to me their body might try and sweat all that extra energy away.

Here some information on this:
https://www.vooner.com/a-beginning-to-thermodynamics-and-enthalpy-when-applied-to-vacuum/

At atmospheric pressure (14.7 psia), the latent heat of vaporization is about 970 BTU/lb. In a rough vacuum (for example, at 1 psia), that value jumps to about 1,036 BTU/lb. Why? In a liquid, molecules are held together by internal bonds. At lower pressures and temperatures, the molecules have less “natural” kinetic energy, so you must add more external energy to break them apart and turn them into a gas.
...
Evaporation (The Cooling Effect)
In a vacuum system, evaporation is often used for cooling. Since the water “wants” to evaporate at a lower temperature, it will pull the necessary latent heat (~1,040 BTU/lb) from its own liquid mass or the surrounding equipment. This causes the remaining liquid to drop in temperature rapidly, a process known as Auto-refrigeration.

The question is whether the body would sweat sufficiently under these conditions.

 

[Filip Larsen]

I understand from the Wikipedia page about effects of spaceflight on the human body that there are several effects that in short time will be fatal, the precise set of effects depending on whether the decompression is explosive or slow. Like in diving and aviation, the "main killer" effect seems to be loss of consciousness in the sense that if you pass out due to low oxygen pressure inside of 10-15 sec then you only have that much time to become aware and take own actions to survive, and perhaps 1-2 minute for someone else to come rescue and re-pressurize your body.

For diving I belive the lower limit for oxygen partial pressure pO₂ in the air supply is around 16 kPa in order to maintain around a pO₂ above 10 kPa in the arterial blood stream. Below that you will almost surely start to loose cognitive functions and eventually pass out. For comparison, the pO₂ in normal air at 1 atm is around 21 kPa. In diving, shallow-water blackout can occur very fast (i.e. you go from conscious to unconscious within 1-2 sec) because the blood stream pO₂ drops below the limit even though you body is still in around one atmpheric pressure. I therefore assume that a significant body pressure drop most likely also will give rise to a significant blood stream pO₂ drop. E.g. if you had been breathing normal air at 101 kPa, then you may start to pass out when the (air) body pressure drops below 70-80 kPa whereas if you had been breathing pure oxygen at 21 kPa the body then the same should happen around 16 kP. Thus, I would guess that the small pressure difference a normal body would be able to retain for a short while between external pressure (near vacuum) and internal arterial pressure is going to be much more "helpful" in retaining arterial pO₂ in case you have been breathing pure oxygen in low pressure. I still think you will pass out inside 10-15 sec even with pure oxygen, but that is better than the 1-2 sec I venture you would stay conscious in vacuum after breathing 1 atm air.

 

[Roberto Pavani]

If protected by everything else but only exposed do "near zero pression":
https://it.wikipedia.org/wiki/Sojuz_11

 

[Baluncore]

I expect the first effect of the vacuum would be to collapse the lungs, which you could not fight. That would immediately end gas exchange, but there would be sufficient oxygen in the blood for continued consciousness. I would expect the irreversible killer to be the rise in CO₂, with acidification of the blood.
Would the vacuum pull dissolved CO₂ from the blood, even with the lungs collapsed?
Would O₂ also be removed from the hemoglobin in the blood, through collapsed lungs?

 

[DaveC426913]

I expect the first effect of the vacuum would be to collapse the lungs, which you could not fight.

This is what I was thinking too. I don't think scuba gear would help.

 

[Filip Larsen]

I expect the first effect of the vacuum would be to collapse the lungs

Assuming the person is quick enough to realize what happens and is able to retain a slight (over-) pressure of air in his or hers lungs then I don't see why lungs should (structurally) collapse. In diving lung collapse is associated with free diving too deep, where (in effect) the lung has significant under-pressure relative to the external pressure.

I would expect the irreversible killer to be the rise in CO2

Why would CO₂ transfer slower from the blood to the (near vacuum) lungs? In "normal" situations, CO₂ transfer to the lung as long as its partial pressure in the blood relative to that in the lungs are above some limit.

 

[DaveE]

Interesting thought. If someone were to exit the ISS with only a scuba tank for air, and maybe a mask to keep their eyes from drying out, how long would they then survive?

General googling says the irradiance at the ISS is ≈1360 watts/m² and this site says a 1m² black body @ 90°F emmits ≈500 watts. This mean the person would actually warm up!

We should probably give them a water bottle as it seems to me their body might try and sweat all that extra energy away.

Sorry, y'all missed my point. Scuba divers know that reduced pressure creates air emboli in you blood.

Anyway, I don't think you can pressurize your blood with compressed air in your lungs. I don't think the alveoli are strong enough to withstand much pressure difference. Scuba divers also know not to hold your breath as you ascend.

 

[Hornbein]

Sorry, y'all missed my point. Scuba divers know that reduced pressure creates air emboli in you blood.

Anyway, I don't think you can pressurize your blood with compressed air in your lungs. I don't think the alveoli are strong enough to withstand much pressure difference. Scuba divers also know not to hold your breath as you ascend.

But it's only one atmosphere of pressure. I'd think that isn't enough to cause problems.

 

[Andy Resnick]

If pressure in a vacuum is very low, water can evaporate even at low temperatures, since the lower the pressure, the lower the boiling point.
So, if I were suddenly exposed to the vacuum of space, would my body freeze, or would it expand as the water in my body turned into gas?

There's video of an astronaut experiencing explosive decompression: