Optimal air pressures.. - Which is best? More O2 or more pressure?

Byron · 2002-10-28 08:35:56

Identifing These plot registries have been marked
0041 Manufacture of atmosphere for habitats
0042 Manufacture of atmosphere for greenhouses
0043 Manufacture of atmosphere for specialized applications such as mobile transporters

A thought came to me while I was thinking about the dust problem...what the ideal mixture of gases and pressure should be in Mars-bound spacecraft and in the habs on Mars...

From what I understand of NASA space missions (please correct me if I'm wrong on this) run atmospheres of 300 mb (slightly less than 1/3 sea level pressure) but close to 100% oxygen, as opposed to the Russian space missions which use plain bottled Earth air at terrestrial pressures (like on an airliner.)

The advantages of having lower air pressure in an enclosed vessel or hab are obvious...less force pressing against the inside of pressure-sealed walls, doors and windows. However, having an atmosphere of 100% O2 has its disadvantages as well, as breathing pure oxygen can cause health problems (O2 is a corrosive oxident, even within the human body!), not to mention the increased fire hazards.

So what do you think is best? Keeping the air pressure as low as possible to reduce the strain upon the physical structure of the hab, or keeping the O2 level as low as possible (<50% of the gas mixture), and therefore having higher pressure (>500mb)? Or would a 70/30 O/Ni mix at 400 mb be the most ideal compromise?

Also, what is the lowest air pressure one can have at standard room temp (20C) in order to keep from having to put on a pressure suit? (provided one is using a respirator mask) Places such as greenhouses, etc. would need to be kept at the lowest possible air pressures, but I shudder at the thought of the agricultural specialists having to perform their work everyday in the greenhouses in decidely uncomfortable pressure suits, so what kind of compromise would work best in that kind of situation?

B

Phobos · 2002-10-28 18:21:37

I'm kind of leaning toward not having more oxygen. It could create a problem with flammability if the proportion of oxygen is too high. Of course it's possible NASA has solved this problem already or I doubt if they'd be using such high oxygen proportions. But just using my gut, I think it'd be better to use gases in proportions that we're used to here on Earth since that combination of gases seems safer. I'd hate to see someone brushing the Martian dust off their suit only to cause an electrostatic discharge and blow up the hab (yeah I know they'll use vaccuums or something for that purpose, just a figure of speech. )

RobS · 2002-10-29 11:43:22

Someone must have this information somewhere. The Mars Direct plan proposes about 1/3 or 1/2 of an atmosphere, with oxygen pressure the same as earth and less inert gas (say, 40% O2 and 60% N2 at half an Earth atmosphere of pressure). For the pressurized rover (which is often depressurized) and space suits, Mars Direct proposed pure oxygen at a low pressure.

I can think of three problems with low air pressure: (1) sound does not transmit as well, so you can't hear as easily; (2) cooking is more complicated because of the lower boiling point of water; and (3) your farts would last longer (because the same mass of gas takes up a larger volume). My, my, think of the jokes. . .

-- RobS

Sir Bloxham · 2003-01-14 17:04:11

All the more reason to put the crew on a 100% Spirulina diet

orionblade · 2003-01-20 12:47:02

Hey, i just read the first post and part of the second, so if some of what I say is duplicitous, just let me know...

The reason we use pure oxygen is the same reason submarines use an oxygen/helium mix (research subs where you need to get in and out all the time) because of the "bends". The bends are caused when nitrogen literally fizzes out of your blood like carbon dioxide in your soda. This results from a rapid pressure change, so instead of the nitrogen simply dissolving out of the blood and diffusing through the lungs, it forms bubbles which can go to the brain and other vital organs and cause a gas embolus and you literally drop dead for no apparent reason. Just so you know, an embolus is anything that causes a blockage in a blood vessel, such as a blood clot, air bubble, misguided catheter, etc. My mother had/has pulmonary emboli, and this is a condition where someone creates blood clots which go to the lung (hence pulmonary) and cut off the blood supply to varioius parts of the lung. In her case, three out of five lobes were completely collapsed, and two of the clots were large enough that they should have collapsed both lungs, and she would have experienced instantaneous cardiopulmonary failure.

This is why we use pure oxygen. In the event of explosive decompression, assuming our folks are in suits, the pressure change would be survivable, but only if there is no nitrogen in the atmosphere. Running your habs at the currently used pressures of roughly 10 psi, which is about 2/3 of our sea level 14 psi, the pressure drop felt in the suits would still be 4-5psi. This is way too much pressure change to experience without getting the bends. The suits would have to repressurize very rapidly to prevent medical problems. On russian vehicles, if a spacewalk is to be attempted, decompression has to occur before the walker can go out into space, since the pressure would drop from the sea level pressure, and since it's bottled air, he's breathing 70% nitrogen. American space walkers don't have to worry about that, but they do have to worry about not smoking, not letting plastics get too hot and outgas, and potentially spontaneously combusting, and you can't leave oily rags lying around. Of course you don't really encounter oily rags in a space environment, but on mars you might, if you had to work on the rovers...

So to answer your questions, we use 10psi air supply on the shuttle/ISS, 14 psi on the ground, and we use pure oxygen because we don't want to get bent.

I would suggest using an 80/20 mix of oxygen/helium like what divers use when going really deep. This would limit the risk of fire, while making us sound really funny. I would also reccomend that if a rover is taken to mars, since we'll need to use it for a year or thereabouts instead of 2 weeks like in apollo, we need a garage. MOLTOV will be testing out a few things to see how feasible it will be to dig a 6 foot deep trench in which to inflate a garage type structure. I got the idea from this indoor tennis court that you simply inflate over an outdoor court, and you have an instant climate controlled dome that kinda looks like those things in the X-files movie (you know, the bees in the middle of the corn fields...?) Anyhow, on earth you can afford leakage, so you just have a big blower kick on when it starts dropping pressure, but on mars you might be able to afford leakage, since gravity is only 1/3 as powerful, and there's less air pressure pushing the thing in... if you simply pumped it full of ambient martian air at a few extra PSI, then all you'd have to worry about sealing would be the inside surface which could be completely separate and replaceable. kinda like putting two ziplocs inside one another, then inflating the outer one. Anyhow, this way you could simply depressurize the interior, drive the rover in, zip the door shut, repressurize, and work on your rover if you needed to. There would have to be a reservoir though, if you didn't want to lose alot of helium gas. The unfortunate thing is you can't use CO2 for a buffer gas since it's toxic above about 1%, and there's apparently plenty of CO on mars, and that's toxic at much lower concentrations. Let's keep brainstorming though.
Happy thinking,
Rion Motley

Shaun Barrett · 2003-01-24 02:34:53

Hi everybody! I've been away a while ... busy with stuff.

Byron writes:-

Also, what is the lowest air pressure one can have at standard room temperature (20C) in order to keep from having to put on a pressure suit? (provided one is using a respirator mask)

Hi Byron! The room temperature isn't really the problem - it's a human's body temperature that matters. The fluids in the human body are normally at 37 deg.C, at which temperature water boils when the ambient pressure is approximately 65 millibars. So, theoretically, if your greenhouse is not inflated to a pressure of at least 65 millibars, your Martian horticulturist will notice problems with his/her body fluids boiling away!
But the problems don't stop there. Even if our intrepid gardener ensures that the ambient pressure in the greenhouse is kept at 100 millibars and that a respirator is used, we have another obstacle.
About 21% of Earth's atmosphere is oxygen, so oxygen provides about 210 millibars of our standard 1000 millibar atmosphere, and human metabolism runs normally with that partial pressure of O2. (Apparently, we can function on 180 millibars of O2 but it's not something you'd want to do routinely.)
The new problem for our gardener is now obvious: The minimum pressure of pure oxygen required in the alveoli of his/her lungs is 180 millibars. But the pressure on the outside of the chest cavity is only 100 millibars! (Ambient pressure inside the greenhouse). If the respirator is a tight fit on the face, the first deep breath of 180-millibar-oxygen will probably rupture both lungs!!

I know, I know ... I've painted a dramatic picture! But I hope it illustrates the point.
And the point is that the realistic minimum greenhouse pressure, if you don't want to wear a pressure suit, is going to be 210 millibars of almost pure oxygen (you'll need CO2 for the plants, of course).

By the way, that's still nearly 2.2 tonnes per square metre of the greenhouse fabric. So it'll need to be a tubular structure of pretty durable material.

orionblade · 2003-02-12 10:54:59

yes, of course it's your body temperature that matters... However, I did think about the plants. If you wore a pressure suit, and used martian atmosphere for the greenhouse atmospehere since plants eat CO2 for lunch (literally) you'd THEN have to worry about the ambient temperature. The plants would of course have to keep from freezing, but if you got them too warm, and the pressure was significantly reduced, you would wind up with exploding/freeze dried plants, since the fluids in their tissues would boil off. If you use a pressure suit then, your temperature and pressure worries are not over by a long shot. I don't really see the problem with working in a pressure suit, I've done quite a bit of work with bees and gardening using heavy gloves, since I grow blackberries, and I decided to use my beekeeper's gloves to do some harvesting and trimming of some plants, and It's quite easy to work with carrots and the like, especially in a hydroponic environment.

You can select plants with large fruiting bodies for greenhouse population on mars, such as carrots, large radishes, broadleaf lettuce and cabbage (for those with intestinal fortitude and a predisposition against gassyness...) and various other greens. Things like broccoli are easily cut with a sharp knife, and are large enough to not be a problem with bulky gloves. All sorts of choices can be made to accomodate a pressure suit in the greenhouse, but it'd be neater than sliced bread to walk around in shirtsleeves tending a garden and look down and see martian soil under your feet, and look through clear plastic at olympus mons rising in the distance.

as far as constructing the greenhouse, I think burying the whole structure except the very top is a fairly good idea, since you then reduce the strain on the entire structure to be local to the roof. The rest of the structure can translate the stress of inflation pressure to reinforced bands that line the greenhouse structure, and the roof is the only part that would bear that significant weight of 2 tons per square meter. If the rest of the greenhouse can be made of polyethylene, i don't see why you can't have a large flat or curved roof of interlocking polycarbonate panels which could be pre-prepped with a thin strip of cold set epoxy on a dovetail joint, and then when the whole thing is landed and unfolded for inflation, you simply peel off a piece of film on each tongue and groove or dovetail joint and slide them together, and the pressure of inflation forces the panels together, mixing and setting the epoxy. might be a lil complex, but i'm not sure how else to get around the vast stress that high pressure environments induce on the inside of the thin greenhouse structure.

Take care all,
Rion

RobS · 2003-02-12 14:13:29

Partially buring the greenhouse also helps reduce exposure to radiation and helps insulate against the cold (once the ground around the greenhouse has warmed up, at least). You probably need to maintain air pressure high enough to prevent water from boiling in leaves heated by exposure to the sun. I suspect in the sun leaves could get as high as human body temperature (a strong fan might solve the problem, though). Also, one would need to keep two other things in mind:

1. You need an atmospheric pressure higher than the vapor pressure of water, because the water vapor pressure will rise to that level and you need "room" for the CO2.

2. Plants need oxygen at night when there is no sunlight to power them (they do breathe the way we do at night) and even during the day they probably need some. So one could not use pure Martian air, and research is necessary to find out how much O2 our green friends need. Probably not much, but since they evolved in 21% O2 atmosphere, the chemical pathways for obtaining the oxygen may not be efficient enough to function in low oxygen conditions.

-- RobS

dicktice · 2003-02-12 16:33:55

Two queries:
(1) I have never understood the importance of nitrogen gas to breath. Something to do with partial pressures...?
(2) Pressure suits, in which "pressure" applied to the body by means of elastic characteristics of the suit material itself (mentioned from time-to-time in other forums) are not suggested for solving the above-mentioned pressure conundrums--where the atmospheric pressure needs of plants conflict with those of the human horticulturists. Why not...?

Shaun Barrett · 2003-02-13 07:35:30

Hi Dicktice!
You don't have to have nitrogen in your air. Up to 1 atmosphere of pressure (1000 millibars), you could breathe pure oxygen without ill effects - though, apparently, oxygen becomes toxic at a pressure or partial pressure of 2 atmospheres.
The need for an atmosphere of 1000 millibars of pure oxygen is never going to arise, of course, and would create a tendency for things to catch fire easily anyway. If you're going to use pure O2, you can get away quite happily with only 300 millibars for physiological purposes - and your fire risk becomes manageable.
Unfortunately, at 300 millibars ambient pressure in your hab, you're only ever going to get a lukewarm cup of coffee because water will boil at a lower temperature!

As far as elastic pressure suits are concerned, I'm not sure anyone has produced a successful suit of that type yet.
We had a discussion in another thread about suit design, and we were all in favour of a lightweight, clinging type which would least restrict movement. So far ... there isn't one! (I think.)

Phobos · 2003-02-13 13:22:02

So, theoretically, if your greenhouse is not inflated to a pressure of at least 65 millibars, your Martian horticulturist will notice problems with his/her body fluids boiling away!
But the problems don't stop there. Even if our intrepid gardener ensures that the ambient pressure in the greenhouse is kept at 100 millibars and that a respirator is used, we have another obstacle. ....
If the respirator is a tight fit on the face, the first deep breath of 180-millibar-oxygen will probably rupture both lungs!!

When it comes time to recruit farmers for our colony I'd suggest not putting Shaun in the PR department. Being boiled in your own juices doesn't exactly sound like a benefit.

but it'd be neater than sliced bread to walk around in shirtsleeves tending a garden and look down and see martian soil under your feet, and look through clear plastic at olympus mons rising in the distance.

Now that belongs in a brochure to entice future Martian farmers to jump on the cycler! Sounds a lot more attractive than being boiled alive!

Euler · 2003-02-13 22:10:56

Humans don't need nitrogen in the atmosphere, but it is necessary to support a normal ecosystem. Plants need Ammonium(NH4) and Nitrate(NO3) in order to grow. Normally, they get the these compounds from nitrogen fixing bacteria that convert atmospheric nitrogen to the forms that plants can use. If there were no nitrogen in the atmosphere, there would not be any nitrogen fixing bacteria, and plants would be unable to gain essential nutrients.

orionblade · 2003-02-14 13:28:54

The biggest thing that nitrogen does for you is keep you from burning up. I don't like nitrogen in breathing air, since it is what causes the bends, with pressure changes causing nitrogen to either become dissolved in, or to precipitate out of your blood. Nitrogen Embolus is quite fatal, and is why subs use helium (not U.S. Navy subs, but rather research subs and the like). You sound funny, but it's doable. I think there should be another gas you could use other than helium since it is rather hard to come by on mars, perhaps argon or something, but you really need a noble gas since anything else by definition would be reactive and have a biological function. (definitely don't want chlorine as a buffer gas...). Nitrogen could work but I guess you could "cut" it with some helium so that you minimize the effects of fast pressure changes. If you get a breach in the hab, it could be slow enough to not flash boil you, but if unnoticed you could experience a rather quick pressure change that would give you the bends. Surviving a hull breach only to die of the bends is definitely NOT something to put on a brochure.

As far as burying the greenhouse, yeah, you get radiation protection for everything except what's pretty much directly overhead, and impact and wind damage are reduced to ONE face of the greenhouse, which could have a sacrificial, replaceable, polyethelene skin over your polycarbonate paneling. This would erode pretty quickly in a dust storm, but it would keep the underlying structural polycarb from getting toasted.

NITROGEN and OXYGEN in the greenhouse:

You don't need to put oxygen in the greenhouse to start it, since the plants are going to generate WAY more O2 during a day than they need for a night's metabolic activity. Plants actually need some of the oxygen they create all the time, since chloroplasts make sugar, and sugar is essentially burned to get ATP. I beleive it's hydrolysis of glucose that generates ATP most efficiently, and this occurs in mitochondria, which need oxygen. In any case, nitrogen would also be obviated, since you're (hopefully) using a hydroponic system for most of your plants, and you'll already have fixed nitrogen for the plants to use, since the nutrient solution has nitrates in it. Sure there's some loss, but i'd rather have it pre-mixed than have a hard to predict nitrogen sink hooked up to our life support systems. Eventually you could condition martian soil, perhaps as simply as warming it up and adding a little water to kill any peroxides that are present, and use that as your potting mix, which with some aggregate can still utilize hydroponic techniques for irrigation and fertilization. I don't like the idea of introducing microbes on mars any more than we have to, since of course humans are walking petri dishes, but you still want to keep it contained within your suits. UV radiatoin should smoke any microbes on the outside of the suit, so it'd probbably be a non issue, but when you start using nitrogen fixing bacteria, you could be extincting a local species that is yet undiscovered. Who knows? Safe bet is the containment route (damned reds...) to keep contamination to a minimum.

I think that's all the issues i wanted to address for you, but I do wanna say thanks for the quote, and maybe i'll put it up on my website... so anyhow, take it easy y'all, and look for a post from me about my up and coming website, we'll have a couple engine test videos for you (i'm a bit of a pyro... shhhh!) :angry:

dicktice · 2003-02-16 10:22:04

Orionblad: I must say, you've covered any further questions I could have imagined regarding nitrogen in the atmosphere for the needs of the Mars settlers. This society has such a great bunch of members, as far as obtaining needed information is concerned. The simpler (dumber?) it seems that my questions are, the more interesting and complete the answers you post in response.... I wonder if my question were: "Duh, anyone?" what might be the response? (The mind boggles.)

HeloTeacher · 2003-03-07 11:07:24

Nitrogen doesn't stop the burning process, reduced partial pressure of oxygen does. If for no other reason than mission mass the absolute minimum atmosheric pressure should be maintained in the spacecraft and hab. Using a low pressure 100% oxygen system would reduce the complexity of equipment to store and process the atmosheric components and again, reduce mission mass. Additional gases should only be included for physiological requirement or to enhance other mission objectives. I do not know what these would be. That is for the mission planners and the guys who write the cheques.

If we really want to see a cost effective mission, then we need to start simplifying at all levels and reducing the total mission mass to something in line with what is commercially available in the near term.

RobS · 2003-03-07 21:38:28

I've been thinking about this and wonder whether an optimal atmosphere isn't something with about 3/4 of the oxygen at sea level and half again nitrogen or argon, for a total of about 25% of Earth sea level pressure. People living at high altitudes adjust quite successfully to lower pressures; their blood has more red blood cells to carry the oxygen around. If the oxygen pressure were lowered slowly on the flight out, people would adjust. If someone suddenly needed more oxygen, an oxygen mask could deliver almost twice as much to them because there would be no nitrogen or argon.

Maybe our could do without the inert gas, but no one has done that yet, so I suppose there's a reason for it.

-- RobS

dicktice · 2003-03-08 09:55:33

Our...what...could do without the inert gas: bodies, metabolisms...? It's driving me crazy to know what you mean!

RobS · 2003-03-09 15:36:58

I have no idea why NASA and the Russians have included inert gas in the air of their vehicles, but they have, and they know that eliminating it makes the vehicles lighter in mass.

--RobS

RobertDyck · 2003-05-22 20:24:48

For those still interested in spacecraft air pressure, I had a talk this week with the flight surgeon of the Canadian Space Agency; he often works at mission control in Houston. He said that although the current EMU and Orlan suits used for EVA do not use minimum pressure, it has been common to inflate suits to 2.5 psi with pure oxygen. The lower the pressure, the easier joints move. However; the greater the difference between habitat pressure and suit pressure, the longer the oxygen pre-breathe necessary before decompression. He also said they are looking at argon as the inert gas instead of nitrogen because argon is less soluble in blood. The less inert gas dissolves in blood, the less pre-breathe time you need to get rid of it.

Inert gas is used in breathing air for a few reasons: it moderates combustion so is less of a fire hazard, it permits increased pressure without causing oxygen toxicity. Pressure too low causes dehydration of lung tissues, so you require high humidity and the astronaut must drink a lot to prevent tissue damage. The flight surgeon also pointed out that pure oxygen results in alveoli completely collapsing on exhalation. Once completely collapsed the water surface tension seals it closed. It takes a great deal of effort to expand alveoli once collapsed. In fact, he said patients brought in to emergency breathing pure oxygen often get more oxygen in the blood once a little inert gas is added to the breathing air to prevent patient lungs from completely exhaling/collapsing. He also criticized the ISS selection of 14.7 psi pressure; he felt the 5.0 psi of Apollo and Skylab was more appropriate. Since the current EMU and Orlan spacesuits use pressure relatively close to 5.0, the difference in pressure between cabin pressure at 5.0 and suit pressure would mean pre-breathe would be completed during review of the safety check list.

One complicating factor is horticulture. One paper presented a study of an alpine plant grown in low pressure. It exhibited drought behaviour despite the fact it had plenty of water. Plants exhibit various strange behaviours at various pressures. I believe one reason the ISS has pressure equal to Earth at sea level is for biological plant studies. Those researchers (and there were a few) who studied plants in low pressure are looking for a way to operate a greenhouse on Mars.

I have just returned from the 14th Humans in Space symposium run by the International Academy of Astronautics. Wonderful symposium: I was able to talk to CSA, NASA, ESA, and NASDA personnel, as well as university researchers, contractors, etc. I talked to a few astronauts and had a few meals with them. A group of university students presented a paper why NASA needs the focused goal of sending a manned mission to Mars. I presented a paper on my idea for a life support system. It was very educational and a lot of fun. The scenery in Banff was beautiful, and the university students took me with them bar hopping one night; I was able to dance with the girls. (Um, never mind.) But I did make a few contacts.

Shaun Barrett · 2003-05-23 00:38:16

Thanks, Robert, for the interesting post about drinking and dancing with girls.

[P.S. The other stuff you mentioned was OK too. ]

RobertDyck · 2003-05-24 00:22:01

Thanks, Robert, for the interesting post about drinking and dancing with girls.

Well, at the BBQ when I suggested line dancing because that's where the young girls are, Hammy said he would live vicariously through me. I didn't do well at line dancing, (I used to, I guess I need practice), but if it gets back to Hammy that I quoted him, I would like to add the message that I did go dancing with the same girls at the bar later that night.

Bill White · 2003-05-24 13:47:34

One complicating factor is horticulture. One paper presented a study of an alpine plant grown in low pressure. It exhibited drought behaviour despite the fact it had plenty of water. Plants exhibit various strange behaviours at various pressures. I believe one reason the ISS has pressure equal to Earth at sea level is for biological plant studies. Those researchers (and there were a few) who studied plants in low pressure are looking for a way to operate a greenhouse on Mars.

Do you recall any comment on a possible difference between low overall air pressure versus lower CO2 partial pressures?

RobertDyck · 2003-05-24 15:53:15

Do you recall any comment on a possible difference between low overall air pressure versus lower CO2 partial pressures?

I'm afraid not. I only attended 3 presentations regarding plant growth in hypobaric chambers. One covered the facility itself, a second about spinach plant recovery when pressure was restored after reduction to 10 kPa. The other group presented a paper regarding gene expression and compared activated genes to plants grown in drought conditions. None of these presentations varied atmospheric gas concentrations. If you want, you can browse the symposium program and click on a blue session title to see the list of papers. I can look up the abstract of any paper you want in the proceedings book.

dickbill · 2003-05-25 10:19:42

is there some long term genetic effects reported ?

High oxygen pressure is toxic for a long period, I don't know exactly the mecanism, it could be because of interferences with the mitochondrial oxidization/respiratory chain, unable to use all the O2 available. But beside that, free oxygens radicals created in the cells are known to be highly mutagenic. A physiological adaptation would have to take place to be able to deal with long term (the all life ?) presence of these radicals, otherwise, the mutation rate would be increase. So it's reasonnable to expect some genetic effects on people or animals who live in high O2 concentration.

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#1 2002-10-28 08:35:56

Re: Optimal air pressures.. - Which is best? More O2 or more pressure?

#2 2002-10-28 18:21:37

Re: Optimal air pressures.. - Which is best? More O2 or more pressure?

#3 2002-10-29 11:43:22

Re: Optimal air pressures.. - Which is best? More O2 or more pressure?

#4 2003-01-14 17:04:11

Re: Optimal air pressures.. - Which is best? More O2 or more pressure?

#5 2003-01-20 12:47:02

Re: Optimal air pressures.. - Which is best? More O2 or more pressure?

#6 2003-01-24 02:34:53

Re: Optimal air pressures.. - Which is best? More O2 or more pressure?

#7 2003-02-12 10:54:59

Re: Optimal air pressures.. - Which is best? More O2 or more pressure?

#8 2003-02-12 14:13:29

Re: Optimal air pressures.. - Which is best? More O2 or more pressure?

#9 2003-02-12 16:33:55

Re: Optimal air pressures.. - Which is best? More O2 or more pressure?

#10 2003-02-13 07:35:30

Re: Optimal air pressures.. - Which is best? More O2 or more pressure?

#11 2003-02-13 13:22:02

Re: Optimal air pressures.. - Which is best? More O2 or more pressure?

#12 2003-02-13 22:10:56

Re: Optimal air pressures.. - Which is best? More O2 or more pressure?

#13 2003-02-14 13:28:54

Re: Optimal air pressures.. - Which is best? More O2 or more pressure?

#14 2003-02-16 10:22:04

Re: Optimal air pressures.. - Which is best? More O2 or more pressure?

#15 2003-03-07 11:07:24

Re: Optimal air pressures.. - Which is best? More O2 or more pressure?

#16 2003-03-07 21:38:28

Re: Optimal air pressures.. - Which is best? More O2 or more pressure?

#17 2003-03-08 09:55:33

Re: Optimal air pressures.. - Which is best? More O2 or more pressure?

#18 2003-03-09 15:36:58

Re: Optimal air pressures.. - Which is best? More O2 or more pressure?

#19 2003-05-22 20:24:48

Re: Optimal air pressures.. - Which is best? More O2 or more pressure?

#20 2003-05-23 00:38:16

Re: Optimal air pressures.. - Which is best? More O2 or more pressure?

#21 2003-05-24 00:22:01

Re: Optimal air pressures.. - Which is best? More O2 or more pressure?

#22 2003-05-24 13:47:34

Re: Optimal air pressures.. - Which is best? More O2 or more pressure?

#23 2003-05-24 15:53:15

Re: Optimal air pressures.. - Which is best? More O2 or more pressure?

#24 2003-05-25 10:19:42

Re: Optimal air pressures.. - Which is best? More O2 or more pressure?

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