Spacewalks and the Bends?

[humanFish]

OK.

Perhaps I'm being slow because it's late in the day, but I came across this curious article about the astronauts on the space station:

http://news.yahoo.com/s/ap/20060405/ap_on_sc/space_station

says that:

"Before beginning spacewalks, crew members usually have to breathe pure oxygen for several hours to purge their body of nitrogen and prevent a condition known as the bends."

I never gave it much thought that astronauts would have to prepare like this but I guess it makes sense, being that the station is pressurized...and space is a vacuum. I guess the nitrogen would come out of solution in a hurry when they leave the airlock.

pretty cool.

 

[wreckchick]

Actually.... since they're in a closed system, I'm not sure how they could get bent unless the little spacepacks operate at a lower pressure than the station itself. I would think their outfits would be like a 1 atm suit.

<shrug>

Rachel

 

[BigJetDriver]

It was found that a "one atmosphere" suit was too cumbersome and stiff. The suits, with their rebreather packs operate at a lowered pressure.

 

[do it easy]

Never having been in space, I can't speak from experience, but I read somewhere, that they are not 1 atm suits- it's more like being on top of Everest, so with that huge a pressure change, they can get bent when they go to lower pressure(?) in the suit.

 

[herman]

Their space suits are actually pressurized to a lot less than 14psia, I forget the exact number but it is in the 3psia range. If they were to use 1atm the joints in the space suit, esp the glove fingers would be almost impossible to bend. The space craft is at 1atm so they have to deco to safely depressurize to the suit pressure. DAN does a lot of space deco research and did a really great presentation at our dive club meeting a while back on space hyperbaric med...there are some bennies for living close to DAN. Fighter pilots can get bent doing fast, high altitude accents also.

 

[Charlie99]

Their space suits are actually pressurized to a lot less than 14psia, I forget the exact number but it is in the 3psia range.

That isn't just an arbitrary number. The 21% O2 in 14.7psi sea level air has a partial pressure of about 3.1psi, so a 100% O2 rebreather needs 3.x psi to give you the equivalent supply of O2.

... and space is a vacuum. I guess the nitrogen would come out of solution in a hurry when they leave the airlock.

They aren't exposed to vacuum. The vapor pressure of water at 37C/98.6F is about 47mmHg/0.9psi. In other words, the boiling point of your blood is less than your body temperature if the pressure is less than 0.9psi.

 

[humanFish]

That isn't just an arbitrary number. The 21% O2 in 14.7psi sea level air has a partial pressure of about 3.1psi, so a 100% O2 rebreather needs 3.x psi to give you the equivalent supply of O2.

They aren't exposed to vacuum. The vapor pressure of water at 37C/98.6F is about 47mmHg/0.9psi. In other words, the boiling point of your blood is less than your body temperature if the pressure is less than 0.9psi.

Thanks for the clarification. makes sense now...but yesterday was different story

I knew I could count on SB members to have all the right answers

 

[DandyDon]

Their space suits are actually pressurized to a lot less than 14psia, I forget the exact number but it is in the 3psia range. If they were to use 1atm the joints in the space suit, esp the glove fingers would be almost impossible to bend. The space craft is at 1atm so they have to deco to safely depressurize to the suit pressure. DAN does a lot of space deco research and did a really great presentation at our dive club meeting a while back on space hyperbaric med...there are some bennies for living close to DAN. Fighter pilots can get bent doing fast, high altitude accents also.

This is why NASA does so much work with decompression, why Dr.Deco - formerly of that part of NASA knows so much, and why I read everything he posts very closely.

 

[Code Monkey]

But I'd think that the pressure of the meat in your body and the skin surrounding it would keep the blood from actually getting to 0psi. If a human was chucked into space with an O2 mask, wouldn't the blood still stay, er, wet? Now, I _would_ expect the tears to boil off the eyes and, possibly, the oil off the skin. I'd also think that you'd want to cover various orafices.

Does anybody know what would actually happen if a human was exposed to 0psi?

 

[Charlie99]

http://www.sff.net/people/Geoffrey.Landis/vacuum.html and

http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970603.html

basically say that one can survive about 1/2 minute exposure the vacuum. In addition to the skin providing some "containment", once you start boiling off a liquid it cools, thereby reducing vapor pressure.

I'm not going to volunteer for the experimental confirmation.