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Old 06-24-2013, 03:15 PM   #11
gjc8
 
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Default Re: Reconciling Martian and Terran environmental needs

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Originally Posted by vicky_molokh View Post
Correct, but the little dragons were assembled differently, and modifying them isn't exactly feasible (at the moment, anyway).
Well, that was specifically addressing the fact that the dragons have no problem with CO2 levels well-below Mars-normal. Since they're something different, it wouldn't necessarily be so. But since THS biotech is clearly up to producing parahumans than can deal with both Earth-normal and Mars-normal levels of CO2, there's no reason to be surprised that the dragons are also capable of handling both Earth-normal and Mars-normal CO2 levels.

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Originally Posted by vicky_molokh View Post
Thanks, this is exactly the sort of thing I was wondering about. Is there a way to measure the level of this fire hazard based on oxygen content? (I'm assuming you mean specifically the %, since partial pressure is no higher than normal.)
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Originally Posted by MEDICAL AND PHYSIOLOGICAL CONSIDERATIONS FOR A HIGH-ALTITUDE MMA SITE
As a general rule, fire hazard decreases as the partial pressure of oxygen decreases, because of the reduced amount of oxygen available for combustion, and increases as the partial pressure of nitrogen decreases, because of decreased nitrogen quenching. Whether or not a particular atmosphere provides increased or decreased fire hazard depends on which of these effects dominate and on the particular material considered for combustion. The NFPA (1993) defines an oxygen enriched atmosphere to have increased fire hazard, in the sense that it will support increased burning rates of materials, if the percentage concentration of oxygen is greater than 23.45/(TPatmos)^0.5...A commonly used atmosphere in the Space Shuttle and Space Station is 527 Torr (10.2 psi, 0.69 atmos.) barometric pressure, 30 % oxygen, which is used to promote nitrogen washout prior to entering the low pressure (4 psi) spacesuit atmosphere for extravehicular activity. Burning rates for a number of common materials have been measured (NASA, 1992) at the NASA White Sands Test Facility in New Mexico in this 0.69 atmos, 30% oxygen atmosphere. It is reassuring that NASA considers the risk associated with this oxygen enriched atmosphere, which has a significantly higher partial pressure of oxygen than the MMA oxygen enriched atmosphere, to be acceptable, even for a permanently manned spacecraft such as the Space Station....
The discussion in the previous paragraph was concerned principally with the fire hazard of solid materials. Common sense requires that flammable gases and liquids must not be used in an oxygen enriched atmosphere....Volatile liquids require careful handling even without oxygen enrichment. Olsen (1995b) has found that volatile liquids ignite more easily on top of Mauna Kea and their vapors spread more readily than at sea-level. This is due in part to the fact that the flash point of volatile liquids decreases as barometric pressure is reduced. The flash points of typical volatile liquids such as benzene and ethanol are about 8C lower at 5000 m altitude than at sea-level (NFPB, Fig 3-5D, 1992).
Emphasis added.
MEDICAL AND PHYSIOLOGICAL CONSIDERATIONS FOR A HIGH-ALTITUDE MMA SITE

.6 bar and 30% oxygen is right on the border of the definition of an oxygen enriched atmosphere provided by that formula.

Last edited by gjc8; 06-24-2013 at 03:19 PM.
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Old 06-24-2013, 03:32 PM   #12
Anthony
 
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Default Re: Reconciling Martian and Terran environmental needs

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Originally Posted by vicky_molokh View Post
Thanks, this is exactly the sort of thing I was wondering about. Is there a way to measure the level of this fire hazard based on oxygen content? (I'm assuming you mean specifically the %, since partial pressure is no higher than normal.)
Yes, the thing about neutral gases is that they absorb heat from a reaction and thus prevent a self-sustaining flame when one would occur in the pure gas. I don't have exact numbers, though; it's just 'more dangerous'. It also tends to mean that you have supplies of compressed or liquid pure oxygen sitting around, which is most certainly a fire hazard.
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Originally Posted by vicky_molokh View Post
Also, what's so surprising about being able to lower CO2 to human-acceptable levels?
Unlike nitrogen, CO2 is quite significantly soluble in water, and forms a weak acid when doing so; something adapted to a certain level of blood acidity would probably notice its absence. Humans are used to about 3 mbar of CO2, and more than about 10 mbar is unsafe long term.

Last edited by Anthony; 06-24-2013 at 03:42 PM. Reason: fixed numbers on CO2
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Old 06-24-2013, 03:39 PM   #13
vicky_molokh
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Default Re: Reconciling Martian and Terran environmental needs

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Originally Posted by Anthony View Post
Yes, the thing about neutral gases is that they absorb heat from a reaction and thus prevent a self-sustaining flame when one would occur in the pure gas. I don't have exact numbers, though; it's just 'more dangerous'.
Something to consider. Though the NASA numbers don't seem to look very different from the ones I'm seeing. Gotta invest in newer fire-extinguishing systems, I guess.

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It also tends to mean that you have supplies of compressed or liquid pure oxygen sitting around, which is most certainly a fire hazard.
I'm afraid there's not much way around that one.

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Unlike nitrogen, CO2 is quite significantly soluble in water, and forms a weak acid when doing so; something adapted to a certain level of blood acidity would probably notice its absence. Humans are used to about 0.3 mbar of CO2, and more than about 1 bar is unsafe long term.
Hmm, thanks for pointing that out. I wonder if they have Filter Lungs like Adraste do (which is probably a really weird solution, but not much more roundabout than some of the other stuff we've found).
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Old 06-24-2013, 03:55 PM   #14
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Default Re: Reconciling Martian and Terran environmental needs

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Originally Posted by Anthony View Post
It also tends to mean that you have supplies of compressed or liquid pure oxygen sitting around, which is most certainly a fire hazard.
Maintaining this setup won't require any more compressed or liquid pure oxygen than maintaining any other spacecraft atmosphere, believe it or not. Oxygen concentrators available today are quite capable of producing a 30% oxygen atmosphere out an Earth-normal atmosphere purely by molecular sieve filtration. The various high-altitude oxygen enriched atmosphere facilities use oxygen concentrators rather than storing pure oxygen.

Edit: Although there will be places in the ventilation system with significantly higher oxygen fractions, where an oxygen concentrator outputs. Significantly less dangerous than compressed or liquid oxygen, but still a hazard.

Last edited by gjc8; 06-24-2013 at 03:59 PM.
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Old 06-28-2013, 03:55 PM   #15
jeff_wilson
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Default Re: Reconciling Martian and Terran environmental needs

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Originally Posted by vicky_molokh View Post
Now, Pressure-Tolerant Lungs (Perks, p.11) are totally awesome, since the perk allows a human to treat Thin atmospheres as Normal, but Normal as Normal too, all things being equal. Which is awesome, since it seems to solve the partial pressure problem all on its own. But this Perk was published waaaay later than all of THS biomods, or even the 4e Bio-Tech biomods. So I'm unsure if it's possible to get it, and how. Yes, I know it's borderline useless for a real Martian atmosphere, but for the midway environment, it seems like a perfect fit. Do you think it's an available biomod in THS, and should it be a difficult one if it is?
I'm sure you can get the equivalent in TS by having a progressive series of lunglets with overlapping pressure ranges. Lower-pressure lobes would be made to collapse harmlessly in in higher pressure, and re-expand autonomously in lower pressure, making restrictive clothing problematic.
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