Scuba in Vacuum

[bonster]

In the flag on the moon thread, a poster mentioned using scuba gear to breath in a vacuum.

If I remember correctly, scuba regulators are designed to deliver air to the lungs at the same pressure as the environment. In a vacuum, the regulator valve would stay closed keeping all the air in the tank.

It's been awhile since I learned how scuba gear works, so I might be wrong. Can anyone offer any insight?

Also, would scuba be effective in low pressure environments, such as the surface of Mars? or the summit of Everest?

 

[Paul C. Anagnostopoulos]

Yes, both regulator stages work by detecting pressure below that of the ambient water pressure. If you suck in with a zero ambient pressure, you can't reduce the internal pressure below zero, so I don't think you'd get any air.

~~ Paul

 

[Mr. Skinny]

I'm curious now. Would you also have to reduce the pressure of the air in the scuba tanks to compensate for the lack of the 14+ psia of atmospheric being exerted on the outside of the tanks?

Seems you'd have to.

 

[Dragonrock]

I'm curious now. Would you also have to reduce the pressure of the air in the scuba tanks to compensate for the lack of the 14+ psia of atmospheric being exerted on the outside of the tanks?

Seems you'd have to.

I think the whole idea of things exploding in space has been hyped up by bad books and movies. There is 14 psi at the surface of the earth but that's not much. The LEM on the Apollo missions had places that were about the thickness of an aluminum can and it never ruptured.

As a side note, if a person were ever exposed to the vacumn, they wouldn't explode. Their body fluids would boil away and they would quickly be reduced to a big piece of space jerky.

 

[EdipisReks]

Their body fluids would boil away and they would quickly be reduced to a big piece of space jerky.

but not that quickly. both US Astronauts and USSR Cosmonauts were exposed to vacuum for short periods of time on various body parts (for instance a glove having a hole). while they experienced severe pain while they were exposed to vacuum, they suffered no permanent damage.

 

[_Q_]

I'm curious now. Would you also have to reduce the pressure of the air in the scuba tanks to compensate for the lack of the 14+ psia of atmospheric being exerted on the outside of the tanks?

Seems you'd have to.

I'm not a SCUBA guy, but I just read that the working pressures for such tanks are something like 3000 PSI. So I think yes, moving such a cylinder from atmospheric pressure to vacuum would result in a 14 PSI greater pressure difference, but I doubt that such would be considered significant (one would need a fairly sensitive gauge to even reliably discern 3000 PSI from 3014 PSI).


Q

 

[Byzantine Magpie]

I think the whole idea of things exploding in space has been hyped up by bad books and movies. There is 14 psi at the surface of the earth but that's not much. The LEM on the Apollo missions had places that were about the thickness of an aluminum can and it never ruptured.

In fact, the pressure inside the LM was only about 5 psi I think, because it was pure oxygen. This, and the low gravity it operated in, allowed the LM to be incredibly delicate.

Another vaguely scary thing about the LM was that while it was being depressurised prior to a Moon walk, the astronauts would sometimes hasten the process by peeling back part of the hatch.

 

[Houngan]

Hmm. Being a scuba guy, I'd have to say that you WOULD get air, because the reg would start to free flow. The second stage of a regulator (the mouthpiece) is designed so that a small decrease in external pressure (you sucking in) causes airflow. The first stage does all the delicate mechanics to keep the pressure on the tank side ever so slightly less than the external. In a vacuum, you have the ultimate lack of pressure, so it will spill its guts. As to whether you would get a breath off of the explosively expanding air, I couldn't say.

H.

 

[Mr. Skinny]

I'm not a SCUBA guy, but I just read that the working pressures for such tanks are something like 3000 PSI. So I think yes, moving such a cylinder from atmospheric pressure to vacuum would result in a 14 PSI greater pressure difference, but I doubt that such would be considered significant (one would need a fairly sensitive gauge to even reliably discern 3000 PSI from 3014 PSI).
Q

Thank you _Q_. I had no idea that SCUBA tanks were that highly pressurized. I somehow thought that it was only a few hundred pounds.

I agree that 14 psia is insignificant.

 

[_Q_]

OK, I can't vouch for the accuracy of it, but here's what HowStuffWorks has to say about SCUBA equipment (including regulators):

http://entertainment.howstuffworks.com/scuba1.htm

I couldn't noodle out their diagram of the "balanced piston" first stage regulator, but found diagrams at http://www.delportdupreez.co.za/diving/equipment/html/first_stage.html that made more sense to me.

Draw your own conclusions as to how this would work in a vacuum environment. It seems to me that the result might depend on the style of first-stage regulator in question, but I'd have to think some more about it, and I probably won't.


Q

 

[daver]

Also, would scuba be effective in low pressure environments, such as the surface of Mars? or the summit of Everest?

Generic SCUBA mix is compressed air. This isn't going to do any good at low pressures--it'd be the same as breathing the outside air, but you'd be hauling around the tank.

However, presumably you're talking about pure O2 in the tank. Air pressure on the top of Everest is about 4 psi if i plugged the right numbers into the formula. Some sort of oxygen boost would work ok at that pressure.

Mars is running around 7 millibars. Pure oxygen at ambient pressure would be pretty much indistingushable from no oxygen at ambient pressure--unconscious within tens of seconds, dead within minutes.

 

[Houngan]

I couldn't noodle out their diagram of the "balanced piston" first stage regulator, but found diagrams at http://www.delportdupreez.co.za/diving/equipment/html/first_stage.html that made more sense to me.



Q [/B]

The easy way to think of it is this:

You've got a tank at BIG pressure.

You've got valve1, which knocks the big pressure down to ambient pressure, minus .0001.

Valve1 knows when to deliver more of the high pressure air by various means, but all are based on the idea that when you go a little deeper, then the pressure offsets a little via a membrane somewhere, which toggles a delivery switch on valve1, which squirts more air into the hose, which closes valve1.

It's a simple negative feedback loop, based on external pressure. When you suck on the reg, you decrease the external pressure, as far as the first stage knows.

H.

 

[_Q_]

Thank you _Q_. I had no idea that SCUBA tanks were that highly pressurized. I somehow thought that it was only a few hundred pounds.

I agree that 14 psia is insignificant.

Skinny,

It was news to me, too - same sort of working pressures as the garden-variety compressed gas cylinders that I treat with such respect.

(Side note: Whenever I see a cylinder of helium in a card shop, grocery store, etc. for filling balloons, I always check to see if they have it chained up or in an appropriate stand. If they don't, I politely bring it to their attention. If they don't respond appropriately, I go off on them.)

For testing, those cylinders (and SCUBA tanks, too, I just learned) are tested hydrostatically on a periodic basis - they "inflate" them with water to something like 5/3 of nominal working pressure, then see how much they recover when they "deflate". So every such cylinder has seen, at least briefly, 5000 PSI.


Q

 

[_Q_]

The easy way to think of it is this:

You've got a tank at BIG pressure.

You've got valve1, which knocks the big pressure down to ambient pressure, minus .0001.

Valve1 knows when to deliver more of the high pressure air by various means, but all are based on the idea that when you go a little deeper, then the pressure offsets a little via a membrane somewhere, which toggles a delivery switch on valve1, which squirts more air into the hose, which closes valve1.

It's a simple negative feedback loop, based on external pressure. When you suck on the reg, you decrease the external pressure, as far as the first stage knows.

H.

Houngan,

Thanks for the additional description. I have at least a passing familiarity with diaphragm-based regulators, so I understand the concept, but was having trouble with the "balanced piston" mechanism. The HowStuffWorks diagram for that one simply stinks. The diagram at the other linked site doesn't stink, and makes sense to me.


Q

 

[Mr. Skinny]

Skinny,

It was news to me, too - same sort of working pressures as the garden-variety compressed gas cylinders that I treat with such respect.

(Side note: Whenever I see a cylinder of helium in a card shop, grocery store, etc. for filling balloons, I always check to see if they have it chained up or in an appropriate stand. If they don't, I politely bring it to their attention. If they don't respond appropriately, I go off on them.)

For testing, those cylinders (and SCUBA tanks, too, I just learned) are tested hydrostatically on a periodic basis - they "inflate" them with water to something like 5/3 of nominal working pressure, then see how much they recover when they "deflate". So every such cylinder has seen, at least briefly, 5000 PSI.


Q

_Q_,

You're preaching to the choir here. I'm a safety engineer in a research laboratory. We have scads of compressed gas cylinders in our facility (all chained or otherwise secured )

I'm also a Board certified Boiler & Pressure Vessel inspector in Ohio. Anyhow, here in the states, hydrostatic tests are performed at 1.5 times the maximum allowable working pressure, so your 5/3 is a pretty close guess. The test does not really test for recovery on "deflation", it just check to see if the cylinder will fail destructively. Water, being essentially incompressible, is used for the test since it is safer than using a compressed gas or the like.

 

[Houngan]

_Q_,

You're preaching to the choir here. I'm a safety engineer in a research laboratory. We have scads of compressed gas cylinders in our facility (all chained or otherwise secured )

I'm also a Board certified Boiler & Pressure Vessel inspector in Ohio. Anyhow, here in the states, hydrostatic tests are performed at 1.5 times the maximum allowable working pressure, so your 5/3 is a pretty close guess. The test does not really test for recovery on "deflation", it just check to see if the cylinder will fail destructively. Water, being essentially incompressible, is used for the test since it is safer than using a compressed gas or the like.

Heh, "destructively."

Every scuba shop I've been to has a picture of a blown tank hanging above the compressor. Instant, awful, rending death.

H.

 

[Mr. Skinny]

Heh, "destructively."

Every scuba shop I've been to has a picture of a blown tank hanging above the compressor. Instant, awful, rending death.

H.

Back in the 70's I worked as a fire protection engineer for an insurance company. If you discovered a nasty situation at an industrial facility, it was refered to as a "Large Loss Possibility".

Once, I was reading the file of an acetylene refilling plant. The top file was a Loss Investigation describing how an acetylene cylinder had fallen over, lost the valve, and subsequently rocketed into a bunch of other acetylene cylinders.

The engineer investigating the losss concluded his report by saying "The Large Loss Possibility previously reported at this facility no longer exists. In fact, the facility no longer exists". I about fell out of my chair laughing.

 

[ChuckieR]

Here's a quote from a USAF site:

When one is breathing pure oxygen at 33,700 feet, the partial pressure of oxygen in the alveoli is the same as the pressure at sea level when breathing air. Above 34,000 feet, the partial pressure of oxygen in the lungs begins to fall below the pressure at sea level, even though 100 percent oxygen is breathed. At altitudes greater than 40,000 feet, the partial pressure of oxygen decreases rapidly and falls below the limit that maintains the body in a physiologically safe condition.

I actually took the Air Force "Physiological Training: Flight" course, part of which involves sitting in an altitude chamber. At high "altitudes", oxygen content aside, it becomes very difficult to breath. You have to change your breathing strategy and really push your muscles in order to get air into your lungs (or, maybe it was to get the old air out of your lungs, I can't remember).

Much above 35K-40K feet, you need a pressure suit.

I guess if they could have gone to the moon with a simple SCUBA setup, they would have done it! But, then, we wouldn't have GORTEX.