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Topic: Acceptable Atmospheres (He, SF6, O2, N)  (Read 19903 times)

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Selena

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Acceptable Atmospheres (He, SF6, O2, N)
« on: September 10, 2005, 09:17:38 PM »
Hello all! :D
I am in the midst of writing a sci-fi book for young readers, but I can not find some of the atmospheric / terraforming information I need.

This book involves terraforming a distant moon, and I need to know what mixtures of gases would be acceptable for a breathable atmosphere. I have come up with the combination of:

Helium 35%, Sulfur Hexafluoride 35%, Oxygen 20%, Nitrogen 9%, and 1% other elements (water vapor, methane, carbon dioxide, etc...).

Would anything detrimental come from this mixture? Am I setting up my future colonists to agonizing deaths? And, Helium and Sulfur Hexafluoride both cause (equal/opposite) changes in speech (fast/slow) - with a balanced mixture of both gases would these effects also balance out?

Any advice/help would be greatly appreciated! Thanks everyone!  ;D

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Re:Acceptable Atmospheres (He, SF6, O2, N)
« Reply #1 on: September 10, 2005, 10:32:32 PM »
Can't use argon instead of something exotic like SF6?  And why can't space people sound like chipmunks on other planets?  Would be cheaper than to find and transport these gases at celestial volumes.
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Offline billnotgatez

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Re:Acceptable Atmospheres (He, SF6, O2, N)
« Reply #2 on: September 10, 2005, 10:37:49 PM »
Typically on earth excluding water vapor and pollution

Clean Dry Air Component  Percent
Nitrogen                  78.084
Oxygen                    20.947
Argon                      0.934
Carbon Dioxide             0.033
Other                      0.002

If there were Sulfur Hexafluoride in the air it would be a very small amount.

Below is from the Internet

Sulfur Hexafluoride is a colorless, odorless, nontoxic, nonflammable gas that is used as an insulating gas in electrical equipment. At atmospheric pressures it sublimes directly from a solid to a gas. Sulfur Hexafluoride is chemically inert and is completely stable in the presence of most materials to temperatures of about +400°F at 392 psig
(+204°C at 28 bar). It is shipped as a liquefied compressed gas at its vapor pressure of 298 psig at +70°F (21.5 bar at +21.3°C). Sulfur Hexafluoride is used for leak detection and as a gaseous dielectric for transformers, condensers and circuit breakers. Sulfur Hexafluoride is highly effective as an etchant in the semiconductor industry. Spectra Gases Material Safety Data Sheets (MSDS) are available for Sulfur Hexafluoride and should be used as guidelines in regard to first aid, methods of storage, handling and general use of Sulfur Hexafluoride.

A material safety data sheet is at
http://www.matheson-trigas.com/msds/MAT22300.pdf

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Re:Acceptable Atmospheres (He, SF6, O2, N)
« Reply #3 on: September 11, 2005, 03:42:29 AM »
Oxygen alone will be enough, without any other gases. It must just have a correct pressure.
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Offline billnotgatez

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Re:Acceptable Atmospheres (He, SF6, O2, N)
« Reply #4 on: September 11, 2005, 06:34:43 PM »
borek et al

http://science.howstuffworks.com/question493.htm

You can get oxygen poisoning and I think that higher CO2 levels would also cause problems.

Acclimation may be the key need

« Last Edit: September 11, 2005, 06:37:15 PM by billnotgatez »

Offline Borek

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Re:Acceptable Atmospheres (He, SF6, O2, N)
« Reply #5 on: September 11, 2005, 07:27:53 PM »
As long as oxygen pressure doesn't exceed about 150 mm Hg you are on the safe side, that's why I have wrote about correct pressure.

As for CO2 you are absolutly right. Although I don't remember exact number, too high pressure of CO2 makes it impossible to remove it from blood. Fast breathing is not induced by lack of oxygen oxygen intake, but by the CO2 excess. This CO2 excess lowers pH of blood and that's what makes us pant. Thus if there is enough oxygen, but there is a high level of CO2 you pant as crazy and you are not able to do anything.
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Re:Acceptable Atmospheres (He, SF6, O2, N)
« Reply #6 on: September 12, 2005, 08:28:06 AM »
If I remember correctly, terraforming refers to man intentionally engineering an atmosphere.  For what physiological basis would man intentionally introduce sulfur hexafluoride into an atmosphere, a compound that probably does not exist in nature?  It may sound exotic, however, it seems like a useless and energy intensive process.  As Borek indicated a CO2 sink to prevent excessive buildup, nitrogen (or possibly helium or argon as a diluent) and oxygen are all that is needed.

Selena

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Re:Acceptable Atmospheres (He, SF6, O2, N)
« Reply #7 on: September 12, 2005, 09:18:42 AM »
Wow! That was a better response than I had hoped for, thank you all for helping me out.

Dude: As for introducing SF6, I was worried about having helium as the sole buffer gas because I had heard that large amounts (would be 70%) could cause brain damage. Thusly I wanted to lower it, but the only other gases that sounded plausible were argon and nitrogen. Honestly, SF6 sounded cooler, so I started with that. :) Other possibilities that I found are xenon, neon, water vapor, and krypton. Are any of these better for a sole buffer gas?

gregpawin: Would argon be safe in such large amounts? I don't mind people sounding like chipmunks from the helium(kinda cool actually) but thought that I was being clever ;)

billnotgatez: Thanks for the links, and exactly! :) At high levels (70% +) most gases become detrimental, so what doesn't??? Acclimation or gene modification would be the easiest solution to avoid all of this, but I'm looking for something more... pat, know what I mean?

Borek: This question leads away from chemistry and into other scientific areas (sorry ;D), but, is having a sea level atmospheric pressure (far) below 300 milibars okay (breathable)? I was under the impression that humans needed a certain level of pressure to help with the breathing process (as demonstrated by breathing difficulties at high altitudes). What are acceptable sea level pressures?

Thanks again, and I'm sorry if I missed anyone in this! All of your input helps a lot!

Offline Borek

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Re:Acceptable Atmospheres (He, SF6, O2, N)
« Reply #8 on: September 12, 2005, 10:45:08 AM »
I was under the impression that humans needed a certain level of pressure to help with the breathing process (as demonstrated by breathing difficulties at high altitudes).

You were wrong :)

All that is needed is high enough pressure of oxygen so that the blood can be saturated in lungs, and low enough pressure of carbon dioxide. Problems with breating at high altitudes are connetcted with too low pressure of oxygen in most cases. Some people are prone to lungs swelling above 3000 m above sea level (due to low pressure IIRC), but that's relatively small group.

Note that pure oxygen (at the lowered pressure) was used for breathing instead of full atmosphere in the american space program (or was it russian?).

What is interesting here is the fact, that as only the pressure of oxygen is important, 'air' used form breathing by scuba divers contains less oxygen then normal air. In Precontient 3 experiment mix used was 2% oxygen/98% helium at 110 meters - no idea what mixtures are used now at such depths.
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Re:Acceptable Atmospheres (He, SF6, O2, N)
« Reply #9 on: September 12, 2005, 02:29:36 PM »
The problem with having helium at any appreciable concentration is that helium is VERY not dense so a good majority of it will move on out into space unless it is confined.  Even if it is confined, it will likely rise to the top of whatever container it's in making the helium concentration at the bottom noticeably less than at the top.  With SF6 you have the opposite problem.  SF6 is one of the densest gases known and will collect in low lying areas.  It will also collect in one's lungs and will not go out.  After some time, it will take up all the space in people's lungs and suffocate them to death.  Chemically it's not toxic at all, but physiologically it's a very good asphyxiant.  
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Re:Acceptable Atmospheres (He, SF6, O2, N)
« Reply #10 on: September 12, 2005, 02:52:36 PM »
After some time, it will take up all the space in people's lungs and suffocate them to death.

It should be enough to stand on your head for a moment once per hour :)

I have just learned that d stands for David ;)
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Selena

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Re:Acceptable Atmospheres (He, SF6, O2, N)
« Reply #11 on: September 12, 2005, 03:56:35 PM »
Okay, so SF6 is out ;) I don't think mandatory hourly hand stands would be a good part of the founding constitution! ;D

So, if I made it so that helium was continually pumped into the atmosphere, would that work? I am hesitant about using a straight oxygen atmosphere due to the flammability (the same reason it is no longer used by NASA and other space programs). Any suggestions?

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Re:Acceptable Atmospheres (He, SF6, O2, N)
« Reply #12 on: September 13, 2005, 08:03:31 AM »
Why are you not using nitrogen like on earth?

Can argon be used instead of helium?


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Re:Acceptable Atmospheres (He, SF6, O2, N)
« Reply #13 on: September 13, 2005, 08:47:14 AM »
Why are you not using nitrogen like on earth?

I think she just want's it to be different ;)
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Re:Acceptable Atmospheres (He, SF6, O2, N)
« Reply #14 on: September 13, 2005, 09:56:28 AM »
It should be enough to stand on your head for a moment once per hour :)

I have just learned that d stands for David ;)

Yes indeedy.   ;)  So many people think it's for 'drug'.  Damned past history.   ;D
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