View Full Version : Atmospheric pressure and your body
12-30-2002, 09:53 PM
First a little background...during a conversation yesterday someone mentioned that two people are trying to break the all-time freefall height record. The record now, established about 40 years ago by either the USAF or NASA, is over 100,000 feet...around 103,000 IIRC. The guy who did it was testing all kinds of things, not the least of which was the pressure suit he was wearing. (I don't have a link for the video of him jumping, but they did have a camera film him as he jumped).
This jump was done from a balloon, I should add.
Anyway, two people are trying to best this record (both using balloons) and are shooting for something like 110,000 ft. What my friend said was that one of them was going up in a conventional pressure suit, but that the other was NOT going to wear a pressure suit.
Thus the question....can this work? I know why a rapid depressurization (such as ascending too fast while diving or a loss of pressurization at high altitude in an airplane) is bad - the nitrogen in your blood comes out of solution and forms bubbles, which can collect in your joints (OUCH!) or lungs (worse!). But since riding a balloon to 100,000 + feet will be contolled, the rider can get rid of the nitrogen as he ascends or just breathe pure O2, so that can't be the problem.
If he wore a pressurized helmet only, would the partial pressure of oxygen be enough to oxygenate his blood through his lungs? Is a pressure suit even necessary at that altitude for survival or is it just a safety device that SR-71 and U-2 pilots wear in case of a rapid depressurization of their airplane?
What happens to, say, your hand if exposed to a near vacuum? Assuming it doesn't freeze (he will have gloves on), if the drop in pressure is gradual will there be any ill effects at all?
12-30-2002, 10:49 PM
This doesn't completely answer your questions, but have you read the Master's (http://www.straightdope.com/classics/a3_147.html) take on vacuum exposure?
12-30-2002, 11:21 PM
I'm pretty sure a pressure suit would be mandatory. Here is a link I found on the Nasa-Dryden website:
A Brief History of the Pressure Suit (http://www.dfrc.nasa.gov/airsci/er-2/pshis.html)
At altitudes above 50,000 man requires a pressurized suit to be safe in this near space environment. At 55,000 feet, atmospheric pressure is so low that water vapor in the body appears to boil causing the skin to inflate like a balloon. At 63,000 feet blood at normal body temperature (98 F) appears to boil. Just as your ears pop while traveling through the mountains or flying on an airplane, reduced atmospheric pressure at these high altitudes allow the gases in your body to expand to the point where they appear to boil off. At altitudes above 65,000 feet atmospheric pressure approaches that of space, that is the pressurization factors for protective equipment to be used at 65,000 feet are essentially the same as would be required for survival in a vacuum.
12-30-2002, 11:25 PM
Originally posted by pilot141
If he wore a pressurized helmet only.....
I can't comment on pressure at 110,000 but can tell you that wearing a pressurized helmet, depending on the gage pressure, would probably suffocate him. I say this because if the pressure in his helmet were higher than the air around him, there could be a large force on his chest cavity preventing hime from breathing.
I know I have a hard time breathing with my wife standing on by chest and she only weighs 100lb. That would correspond to only about 1 psi across my chest. You'd never catch me putting a pressurized helmet.
In diving school, we were told that coming to the surface while holding your breath would cause your lungs to explode but I don't know what kind of pressure differentials you need for that to happen. In the water, you can get to differentials greatly exceeding the 14psi differential of space really quickly. It might not apply to low pressure applications vs standard pressure.
12-30-2002, 11:28 PM
Yes, I had seen that explanation, but it still doesn't answer the question. Divers ascending too fast have the nitrogen in their blood come out of solution, which can cause embolisms and kill you.
The Soviet astronauts died because of a lack of oxygen - the ground crew thought they were sleeping when they found them. In other words, they looked normal.
My question is, I guess, if you had your head in a pressurized helmet, could you gradually ascend to what becomes almost a vacuum (100,000 feet) without a pressure suit? You need to have your head pressurized in order to get the partial pressure of oxygen high enough to oxygenate your blood (there is an altitude, I don't remember what it is, that even 100% oxygen applied at ambient pressure would not be enough to keep you conscious).
Does a vacuum, if gradually exposed to, adversely affect the human body? If you can still breathe, would your extremeties suffer?
12-30-2002, 11:35 PM
If you had only a pressurized helmet your lungs would be inflated to the pressure of the helmet relative to the outside atmosphere. You would not be able to exhale because your abdominal muscles wouldn't be strong enough to push the air out. Of course your lung tissue would rupture long before that, a risk that SCUBA divers take if they don't remember to exhale as ascending.
12-30-2002, 11:45 PM
JoeyG and billy;
Someday I will learn to preview my posts!
The pressurized helmet would only maintain somewhat normal atmospheric pressure (say, at 10,000 ft) on the guy. The pressure on his lungs (via his chest) would be almost zero. This should make breathing easier, not harder. The pressure in his lungs is the same as the helmet, which is lower than outside pressure. If anything, he would have to work to exhale (contract his lungs with lower pressure outside his body). I agree with the diving examples, and water pressures are much more drastic than air pressures. But even so, the exploding lungs on ascent only happen when you do it too rapidly; this guy is going to take it nice and slow in a balloon.
Yes, I've seen and heard about the "blood boiling". Of course, I can't find out what conditions this happened under. 98.6 degree blood in a petri dish? Of course it will boil. But water in my pot will also boil over the edge when I remove the cover. What about blood vessels? I would suspect that the only point that blood would be susceptible to boiling would be where it is exposed to ambient pressure - normally, through the lungs. But if our intrepid skydiver wears a pressurized helmet, would the blood in the lungs, arms or toes even know the difference?
12-30-2002, 11:50 PM
Originally posted by pilot141
The pressurized helmet would only maintain somewhat normal atmospheric pressure (say, at 10,000 ft) on the guy. The pressure on his lungs (via his chest) would be almost zero. This should make breathing easier, not harder. The pressure in his lungs is the same as the helmet, which is lower than outside pressure. If anything, he would have to work to exhale (contract his lungs with lower pressure outside his body).
Yes, he would have to work to exhale. That was my point. PADEYE used better wording but we are saying the same thing. He would not be able to breathe, or if he was strong enough to do it initially, he would tire and suffocate.
12-30-2002, 11:53 PM
Originally posted by pilot141
But if our intrepid skydiver wears a pressurized helmet, would the blood in the lungs, arms or toes even know the difference?
This brings back memories of hickies in highschool. I had one girlfriend that could leave a deep red mark in about 5 seconds. These hickies were internal bleeding caused by low pressure.
I'm gonna guess that your body would know.
12-30-2002, 11:56 PM
Kittenger rings a bell as the fellow (I'm going to bed so I ain't checking)
Seems to me he was in a pressure suit but his glove failed and his hand became very painful, but it quickly (relatively) recovered after he came back to Earth.
12-31-2002, 12:05 AM
You're correct it was Joe Kittenger. IIRC he actually had some frostbite from the cold during the freefall. He actually broke the sound barrier with his body at high altitude where the extremely low air pressure dramatically reduces the speed of sound.
12-31-2002, 12:10 AM
Padeye and billy,
Thanks for the info. Kittenger is the name I was looking for, he did have a problem with a glove, and he did go supersonic.
In fact, both of these new people plan on going about Mach 1.6 before they start slowing down in the lower atmosphere.
I see now that the pressurized helmet will not work. I think I'll have to find the article (Popular Mechanics I think my buddy said it was in) that said that one of these people was going up without a pressure suit. I can't for the life of me figure out how this could work. My pressurized helmet idea was my last desperate grasp at something other than a full pressure suit.
01-01-2003, 06:39 PM
If you're jumping from 110,000 feet, you'll need a pressure suit.
Here's an article discussing the effects of high altitude on humans (http://22.214.171.124/news/aeromed/181893-1.html)
Joe Kittinger jumped from a balloon at just under 103,000' in 1960. He fell for something over 4 minutes, during which his max speed was (IIRC) over 700 mph. He wore a full pressure suit.
I concur that the pressurized helmet scheme wouldn't work. There's a limit to the pressure difference between your helmet and the rest of you that would still allow you to exhale -- you'd be in trouble far below 100,000'.
It's hard to see how anything other than a full pressure suit would work.
01-02-2003, 05:05 AM
Even with pure oxygen, mountain climbers have trouble on Mt. Everest, and that's "only" 26,000 feet. The article I linked to gives 25,000 feet as a point at which the partial pressure of oxygen in the blood starts to exceed the pressure of a 100% oxygen atmosphere, which would be consistent (allowing for variability in atmospheric pressure) with the Mt. Everest experience. These guys are proposing a skydive from nearly four times that altitude. They're going to need more than a helmet and a little green bottle of 02
Originally posted by Broomstick
Even with pure oxygen, mountain climbers have trouble on Mt. Everest, and that's "only" 26,000 feet.
It's actually just over 29,000'. It has been climbed a number of times without supplemental oxygen, including once (Reinhold Messner, 1980) solo, with no assistance of any kind. But it's generally thought that this is pretty hard on your brain cells.
The article I linked to gives 25,000 feet as a point at which the partial pressure of oxygen in the blood starts to exceed the pressure of a 100% oxygen atmosphere
If you're talking about the altitude at which breathing 100% oxygen will not put as much O2 in the blood as breathing air at sea level, that happens around 36,000'. At about 48,000' even breathing 100% oxygen may not be sufficient to maintain conciousness, even at rest. Above that, you need a pressure suit.
01-04-2003, 03:07 PM
I read that article in Popular Science. I'll admit I'm too lazy to go look it up again, by I believe it said that he would be wearing a partial pressure suit, as opposed to the woman attempting the same jump, who would be wearing a very high-tech full-pressure suit, almost identical to what the astronauts wear.
As for Kittinger, he didn't actually break the sound barrier. He surpassed the speed of sound at sea level, but not relative to his own altitude. The two people attempting this jump, however, WILL actually break the sound barrier. Nobody knows what effect the sonic boom will have on them.
Also, when Kittinger's glove came off, his hand DID swell up like a balloon, to several times its normal size. Ouch! Luckily, the remaining pressure seals on his suit remained intact.
Originally posted by hobbes730
As for Kittinger, he didn't actually break the sound barrier. He surpassed the speed of sound at sea level, but not relative to his own altitude.
I though the speed of sound was lower in a less dense medium, meaning that it would decrease as altitude increases.
01-04-2003, 04:30 PM
You're right Xema...hmmm...
Let me read the article again, maybe it'll explain more.
01-04-2003, 04:38 PM
My mistake. He didn't break any sort of sound barrier, according to the article.
"On the dive that established the world record, Kittinger's glove ruptured, the lack of pressurization causing his hand to swell to nearly twice its size. But he aligned safely, having reached 614 mph (just under the speed of sound at his altitude)."
I've always read that he did in fact break some sort of sound barrier, but maybe that's just an urban myth. Then again, even Pop Sci has been prone to error in the past...
As for the suit, Fournier's partial-pressure suit will use air-bladders to squeeze his entire body and keep it from expanding. Apparently this causes massive bruises, but allows much more flexibility while keeping enough pressure on the chest to allow Fournier to breathe.
I'm confused. I found a couple of sites that said Kittinger's max speed was 614 mph, and that this was just short of the speed of sound. I found a couple of others that said he did exceed the speed of sound; one mentioned a speed of 714 mph.
In any case, it seems clear that he wore a pressure suit. One glove came off or otherwise malfunctioned, but cause no lasting problem.
01-04-2003, 10:57 PM
Speed of sound is lowest at low altitudes. That is why the first attempts were down low, we could not go fast enough to break it at higher altitudes. Back in the days when you could go up front in large airliners, you could sit and watch them going .80 Mach at 33,000 feet and indicate an airspeed of less than 160Kts. They were just above stall. There you are going 600MPH over the ground and about to stall out. Takes some getting used to.
There are fewer air molecules and your speed over the ground has to be faster to make them work right in holding the aircraft up. So, at 100,000 feet you can go real fast and not break the sound barrier. Can a skydiver get to a high enough actual speed to go faster than the speed of sound as he comes into denser air? Donno, but he is not going to need anything to stay warm, his temperature is probably gonna rise. I do not think even in a delta position he will make it unless his attire is tight and slick, flapping jump suits cause much drag.
Water, blood, at 98 degrees, a lot of things will boil at 55,000 feet.
I would have a hard time clearing my ears doing that kind of sky dive as I do at diving with rocks for fast descents, I don't clear easy and this has caused me some problems over the years in emergency situations. I hope these folks don't have a head cold when they try this stunt.:eek:
01-04-2003, 11:12 PM
Umm, not so sure about your statement about the speed of sound. Mach 1 is a HIGHER indicated airspeed at lower altitudes...as you climb, your indicated airspeed decreases in relation to Mach number. You alluded to this in your post, but the numbers were off...not four hours ago I was on my way back from Mexico City at 33,000 ft and .78 Mach. Our indicated airspeed was 280 knots.
As for riding the edge between going supersonic and stalling, I believe the U-2 came closest to this. Even with it's giant non-swept wing at altitudes above 65,000 ft the margin between airfoil stall and sonic shock waves was only a few knots of indicated airspeed.
To complete this hijack: to go Mach 1 at sea level you have to go VERY fast indicated (ie lots of air molecules over your wing and into the pitot tube)...on the order of 700 knots. At 30,000 ft Mach 1 is more like 380 knots indicated.
01-04-2003, 11:38 PM
You're right, I got my indicated airspeed and my go fast tangled up. That is why the limiting Mach # VS the airspeed becomes so important. Not all things should go faster than the speed of sound.
Also, I gather you fly 'big' iron. I never have and have never heard why biz jets can usually run higher Mach #'s than an airliner? Or has that changed in the past few years? Design, or size, or.....??
If you fly of have flown a DC-10, I have a question but would like to do it off board. Would like the scuttle butt on an incident that never made it to the NTSB as far as I know.
01-05-2003, 12:06 AM
That's why these boards are so great...I almost always come away knowing something I didn't know before!
Yes, I fly (relatively) big jets. The cruise speed of airliners and bizjets has everything to do with design, and even more these days with marketing. The early jets (707, 727) were designed to go FAST because, after all, they were JETS. The later generations of designs (MD-80, 757) concentrated more on fuel efficiency and less on flat-out speed. The wing design is usually the limiting factor in speed at high altitude, and airliner designers tried to find the perfect blend of speed and fuel efficiency.
Bizjets run the gamut - from the Citation II (AKA Slowtation) to the Citation X, which cruises at .9 Mach. Different strokes for different folks.
Right now I'm on the MD-80, affectionately know as the "roadblock in the sky" because of our mid .7 cruising speeds.
Haven't flown the DC-10, but have lots of friends that have flown both the DC and KC-10.
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