If You're at the Bottom of the Ocean or in Space...

Most recent answer: 10/22/2007

What would happen to an unprotected person at the bottom of the ocean or in outer space?
- Shawntay
Shawntay -

Well, the rough summary in either case is that the person in question would be very dead, very fast, in a very unpleasant manner. But, since you seem to be looking for a more specific answer than that, let’s take it one at a time. (Let me warn you ahead of time that if you have a weak stomach, you may not be interested in some of the images that this all draws to mind.) First, if a person were to wind up unprotected at the bottom of the ocean...

At the bottom of the ocean, there’s four big things that would happen. (1) It’s cold. Because it’s so cold, the person would experience severe hypothermia, and the body would eventually stop working because of the cold temperature, but this is probably not what would kill them. (2) There’s no air. You can’t breath at the bottom of the ocean. If you can’t breath, your body won’t stay alive for more than about 30 minutes. (Although you’d lose consciousness after about 5.)

(3) The water pressure is very high. The pressure from the water would push in on the person’s body, causing any space that’s filled with air to collapse. (The air would be compressed.) So, the lungs would collapse. At the same time, the pressure from the water would push water into the mouth, filling the lungs back up again with water instead of air. But if there’s no air-filled space to be pushed into, the body would not be crushed. (Part of the problem with the old pressure suits that deep-sea divers used to use was that if they depressurized, the soft part of the suit and the entire body would be crushed into the rigid helmet. This is one of the big reasons that divers don’t use suits like this anymore.)

(4) At high pressures, the chemistry of how the body works changes. If the person did have some way of getting air into their system, their body would immediately undergo what’s called "nitrogen narcosis." This happens because at high pressures, nitrogen is much more soluble in water (or blood) than oxygen is. And especially since air is mostly nitrogen, the blood would become full of dissolved nitrogen. The nitrogen would bind to the parts of the body that need to use oxygen, and the person would literally suffocate from the inside out.

Ok... now, if the person were unprotected in space. (Fortunately, this hasn’t actually happened yet, so we don’t really know exactly what would happen. But here’s the best guess.) In space, the three big problems are (1) no air, (2) there’s no air pressure in space, and (3) it’s extremely cold (much colder than at the bottom of the ocean).
If the person were able to hold their breath, they could probably last for at least a few minutes before they ran out of air (and this would protect them from their lungs freezing, too).

The lack of air pressure would pull outwards on their body, but they wouldn’t blow up the way the people did in "Total Recal." What would probably happen instead is that the blood vessels near the skin would burst, causing their skin to turn a pinkish-red color. But it’s pretty hard to say if it would be the lack of air or the cold temperature that would kill them first.

(mod by mw) The cold would be a less immediate problem, because the thermal conductance of the vacuum is low. The body would gradually radiate heat as infrared waves, slowly cooling down. The other problems would be fatal first.


(published on 10/22/2007)

Follow-Up #1: What are "The Bends"

the bends?
- Anonymous
It's a form of decompression sickness initially observed in deep sea divers.  At great depths under water the excess pressure causes nitrogen gas to be absorbed into the blood.  If the diver surfaces too quickly the nitrogen forms bubbles in the blood which raise havoc in the body.    The effect is similar to when you open a bottle of soda:  there is a fizz of bubbles produced.   Think of that happening inside your blood circulation system...
See for more details.


(published on 07/08/2008)

Follow-Up #2: Effect of water pressure on living things

Would death still occur if a person were standing in one of the deep trenches on the earth, assuming the water was drained away? Or is it the water pressure alone that causes crushing and death?
- Lecia Ellis (age 60)
Kelso, WA, USA

Hello Lecia,

The Grand Canyon is over a mile deep and people cheerfully raft and hike at the bottom.   If you dug a hole in the ground a mile deep near Kelso you could stand at the bottom with only claustrophobia to contend with.   Now if someone filled it with water while you were down there the water pressure would crush you.



(published on 07/09/2014)