though recreational technical divers with lots of money to burn like to use it because it makes them look cool on the boat too. (hope there’s no tech divers here to get PO’d at me…)
Don’t you wind up looking cool at the expense of sounding less then cool?

I think the minimum ppO2 we can survive long term at is about 0.1 ATM (half of what we are used to), but clearly much less can be tolerated for a while. The top of Everest is something like 0.07 ATM ppO2 or a third of what we are used to.

That’s amazing.

I think the minimum ppO2 we can survive long term at is about 0.1 ATM (half of what we are used to), but clearly much less can be tolerated for a while. The top of Everest is something like 0.07 ATM ppO2 or a third of what we are used to.

Ooh. Ack. So first you have one problem, then the other. Nasty.

Apparently that’s what happened in the Apollo fire, too – the capsule reached 29 PSI before it ruptured. Because of the design of the door, rescuers couldn’t get inside until the pressure equalized. Tragic.
Yeah, I read the whole Wikipedia article. I think they copied and pasted half a book.

It doesn’t have to be sudden decompression to form bubbles. I think the answer to your question is that there is much less oxygen, and much of it is bound to hemoglobin or being used. Nitrogen isn’t used in the body, it just sits there. There probably is oxygen in the bubbles, especially in sudden decompression.

Oh, that makes sense. Maybe the O2 is either taken up by red blood cells or by antioxidants. I wonder about helium though? I understand helium is used in some dive mixtures to prevent decompression sickness? Or is that nitrogen narcosis? Sorry for all the questions, I should fire up Google before I bug people

Finally, yeah humans can deal with less. Hillary climed Everest without oxygen,

I still find that hard to believe. I mean, I know people have done it, but it doesn’t seem biologically possible. Dang!

It doesn’t have to be sudden decompression to form bubbles. I think the answer to your question is that there is much less oxygen, and much of it is bound to hemoglobin or being used. Nitrogen isn’t used in the body, it just sits there. There probably is oxygen in the bubbles, especially in sudden decompression. Sorry I don’t have a better answer for that one.

Finally, yeah humans can deal with less. Hillary climed Everest without oxygen,

@65 VinceRN: I think the 4 ATM to 1 ATM would be worse then 8 ATM to 4 ATM. The volume of the air in you lungs/gut/whatever would double going from 8 to 4, it would quadruple going from 4 to 1.
Oops. That makes sense. I should have said 8 to 2. I never was good at math

If suits are pressurized at 4.7 PSI with pure oxygen, that would be more oxygen than is in air at 1 ATM (partial pressure of .32 instead of .21). I guess fire risk inside a suit is pretty minimal though. I wonder why they do that? Seems like far less would work. I’m sure there’s a good reason – the guys doing this stuff are (hopefully) a lot smarter than me.

Wow – can humans deal with even less than 4.7 PSI, if it’s pure O2? I assumed 4.7 PSI was the magic number for pure O2 to be at sea level PP, but I guess not.

Oxygen toxicity doesn’t usually occur breathing 100% oxygen at atmospheric pressure. Patients in hospitals are sometimes on 100% for days or even weeks. The dive tables for maximum operating depth start at 1.2 ATM ppO2. Also, not as much was known about this stuff back then, though some was. And, of course, the fire risk outweights the risk of o2 toxicity by several orders of magnitude. The capsule was in fact pressurized to 1 ATM with pure oxygen, and they had reason to do that, though given what happened some might question those reasons…

If suits are pressurized at 4.7 PSI with pure oxygen, that would be more oxygen than is in air at 1 ATM (partial pressure of .32 instead of .21). I guess fire risk inside a suit is pretty minimal though. I wonder why they do that? Seems like far less would work. I’m sure there’s a good reason – the guys doing this stuff are (hopefully) a lot smarter than me.

As for fire, it’s not the pressure; it’s the air mixture. It’s not typical to think of nitrogen as a fire retardant, but fires on Earth are basically exothermic oxidation reactions, so when only 20% of the air is oxygen, stuff doesn’t burn quite as well. Pure oxygen will lower flash points like crazy, which is why I’ve read that (after Apollo 1) some materials cannot be used for space exploration. In the pure O2 environment either they ignite at too low a temperature, or once they start burning they’re impossible to extinguish. IIRC, Apollo 1 used pure O2 at 5psi. Wikipedia says it was atmospheric pressure, but I couldn’t verify that in the citation and pure O2 at atmospheric pressure would lead to hyperoxia.

Good point. The himalayan natives regularly breath a normal air mix at 1/2 atmo and are still able to do physical labor. Put these people in space, with pure O2 and internal pressure under two psi(hey, I was raised old school) and it’s possible they could not only survive but continue working. The two psi is the cut off point for scuba divers as they rise to the surface. It’s equivalent to rising thru four feet of water. A partial pressure differential of this much results in bubbles forced into the blood stream,,,

Gary 7

http://www.footagevault.com/clip/FTV-0005589

This is actual video of a suit testing accident where the person was exposed to the near total vacuum of space.

This video was shown on a TV documentary about the development of the NASA space suit. The air hose connecting the suit became disconnected. Interviews with the suit tester in the chamber, [Jim LeBlank] showed him talking about how he could feel the moisture on his tongue FOAMING up before he passed out.

The main reason he survived was because safety personal were in an adjoining Anti-Chamber at 25,000+ ft pressure next door to the total vacuum vessel. They were able to open the door connecting the two chambers after the main chamber pressure was raised to match the anti-chamber pressure. That allowed the safety personnel to reconnect Jim LeBlank’s air hose much faster than if they had to repressurize the main chamber to ambient earth pressure.

The show talked about how it normally took 20+ min to raise the pressure back to “normal” from a vacuum but they did it in record time to allow the safety people to begin their rescue procedures.

So, “Jim” lived and was unaffected by his short exposure to a complete vacuum ….. but he passed out very fast and was returned to his O2 feed and normal pressures very fast. This quick and speedy response will most likely NOT be available to someone outside a space ship conducting a space-walk. Micro-meteorites pose a very real risk to spacewalkers and ships in space.

59. Joseph G
“I’ve heard that going from, say, 8 atmospheres to 4 in an instant is just as bad as going from 4 to 1.”

Yep. It’s not the number of atmospheres you begin or end with so much as how much and how quickly it changes. At some point when a pressure change is big and quick enough, it blurs into “explosion”. Movies love to draw out the process for dramatic and gory effects but in terms of lethality, going from 9atm to 1atm isn’t all that different from getting blown apart by a bomb — either way you’re getting hit with a very destructive pressure wave.

“I understand that NASA EVAs are currently performed with pure oxygen at a pressure of just 4.7 PSI, so in that case a depressurization wouldn’t even be as violent as one from one atmosphere.”

No, it’s to save costs, really. Whatever safety you get from lower pressure is washed out by the higher risk of fire due to the pure oxygen environment. Air on Earth is mostly nitrogen. If decompressed properly humans can survive in 4-5psi just fine and don’t need the nitrogen, and a larger pressure difference means much more durability needed in the suits and vessel, adding weight & cost. Higher pressure means the air would have to be mixed with nitrogen or helium to prevent hyperoxia (the opposite of hypoxia – oxygen overdose), which to a space flight is just dead weight. It’s much cheaper to design everything around 4-5psi and haul up pure O2.

That Byford Dolphin accident was part of our training for the hyperbaric chamber. Even scarier was the stuff about fire in a chamber. Fortunately such incidents are extremely rare.
SCARIER?!?
Well, yeah, I guess fire would be a slower way to go, at least. Still, I needed brain bleach after reading some of the medical details of the Dolphin accident…

Question: is it true that the speed and magnitude of decompression is a bigger predictor of barotrauma than the final pressure? I’ve heard that going from, say, 8 atmospheres to 4 in an instant is just as bad as going from 4 to 1. So in the case of space exposure there are two main separate issues to deal with – barotrauma from the pressure drop, and asphyxiation from being unable to maintain enough pressure in the lungs for them to work properly. I understand that NASA EVAs are currently performed with pure oxygen at a pressure of just 4.7 PSI, so in that case a depressurization wouldn’t even be as violent as one from one atmosphere.
A morbid part of my brain has always wondered if you could hook someone up to a sort of industrial-strength heart/lung machine (to keep their blood oxygenated), how long could they then stay conscious in a vacuum, if they were depressurized slowly from, say, 4.7 PSI?
I had a loopy idea for a sci-fi story about space station workers. Sort of the reverse of saturation diving – instead of living underwater for extended periods, these folks would live and work in a vacuum, using advanced biotechnology to keep them alive.

The cold part is fascinating. I had thought it would be much faster, like freezing solid in several minutes, and that fluids would leave you much quicker too. This blog and it’s comments are always a fascinating resource.

That Byford Dolphin accident was part of our training for the hyperbaric chamber. Even scarier was the stuff about fire in a chamber. Fortunately such incidents are extremely rare.

Thanks Wzrd1 for great info, I didn’t know about most of that. Very interesting.

I was wondering if anyone would bring the Byford Dolphin accident up. Certainly that’s more the sort of thing people think of when they think “explosive decompression.”
You should probably warn people about that article, though, especially if it’s near dinnertime. It’s as close to high-octane nightmare fuel as you can find on Wikipedia.

It sounds pretty clear that, while consciousness is lost very quickly, you can survive if pressure is restored within around a minute. So, it’s definitely something you want to avoid, but you probably won’t have the “Watermelon filled with red-paint with a firecracker in it” syndrome that some Hollywood films portray

Carbonated soft-drinks are a good example, of dissolved CO2 coming out of solution, when you’ve opened the bottle. There isn’t enough mass pressure for the CO2 @ earth surface pressure to stay dissolved. In a closed, pressurized bottle however, there is.

Blood is basically the same way with oxygen. Between 3 and 4 pressure/mass pounds of oxygen is required for adequate oxygen suffusion in blood. In fact, historically in most space suits, and sometimes spacecraft , they will just run with 4psi of pure oxygen only. (We’re sitting at 14.7psi of pressure at sea level. Most of it nitrogen, and only 3-4 pounds of oxygen)

Well, when a person is exposed to vacuum, in addition to everything mentioned above, in their lungs there is no longer any pressure to keep the oxygen in solution. So it comes out, rapidly depleting the oxygen in your bloodstream. Basically uncontrollably exhaling the oxygen. This quickly leads to hypoxia-unconsciousness. Useful consciousness is only about 10 seconds.

And the worst part of it, hypoxia is insidious. The human body actually does not pay much attention to oxygen deprivation. Instead, the feeling of suffocation, of needing to breathe is based off carbon dioxide saturation of the blood. At high altitudes, (or vacuum) where mass pressure of oxygen is too low for survival, carbon dioxide has been leaving the bloodstream through the lungs at a rate well ahead of vital oxygen. Thusly with no feeling of suffocation, humans will simply drift off and black out, with little to no physiological warning. (Eventually headache and fatigue would occur, but not immediately)

Hypoxia blackout has claimed thousands of lives of aviators, and a few astronaut types, even with extensive training to recognize emergencies and react, it still ends up getting them.

So yeah nothing cinematically awesome happens if someone gets spaced. They flail for a little bit, pass out, go through a few convulsions where they curl up and then die. Then turn to freeze dried people-jerky over a few weeks. There are even tested space suits and high altitude pressure suits that keep the body at vacuum/ambient pressure, and only provide breathing atmosphere to the head. (Look Up: Partial Pressure Suit or Mechanical Counter-Pressure Suit or Space Activity Suit)

1 atmosphere to 0 atmosphere, not a big deal if you get them back under pressure in a minute or so.
But 9 atmospheres to 1 atmosphere? Now that is a problem. The Byford Dolphin accident.

en.wikipedia.org/wiki/Byford_Dolphin