From: Henry Spencer <henry@zoo.toronto.edu>
Newsgroups: sci.space.tech
Subject: Re: highest pressure a person can take? and lowest?
Date: Wed, 13 Aug 1997 15:40:33 GMT

In article <19970813011201.VAA20882@ladder02.news.aol.com>,
Guff12345 <guff12345@aol.com> wrote:
>How high a pressure can a person take (taking all the time in the world to
>compress)?  I think scuba divers go to 10 atmospheres routinely.  How deep
>do deep, deep divers go?  Deep enough to survive on Venus (100 atms?) if
>we manage to turn off the heat?  Could plants take a cold Venus' 100 atm
>atmosphere?

100atm would be about a 1km dive.  This is well beyond what has actually
been done, but as I recall, pressure-chamber tests suggest that it is
feasible.  The ultimate limit seems to be purely a matter of how much work
it is to move air in and out of your lungs, and with helium-oxygen or
hydrogen-oxygen (!) (yes, really -- the percentage of oxygen is below the
flammability threshold) mixtures, a 1mi (1600m) dive is thought to be
possible.  Nobody's actually tried it...

Plants should have no problem with 100atm.  However, they do need oxygen,
so they couldn't use straight Venus air, even cooled down.

(Yes, plants generate oxygen when in light... but they do not have a
circulatory system to deliver it to where it's needed, and their roots
need oxygen.  This is why you can drown a plant by watering it too much:
the water largely blocks diffusion of oxygen to the roots.  Flooded-field
plants like rice often have air plumbing running down to their roots, but
it connects to the outside atmosphere, not to the photosynthetic areas in
the leaves.)

>Going at it from the other side --  why aren't we focusing on using very
>low pressures in our stations?

It increases fire hazard, it makes air cooling of electronics impossible,
it's possibly unhealthy in the long run, and it greatly complicates
running comparison studies between ground and space (because the ground
side needs to use low-pressure chambers).  Mind you, there would be
something to be said for running at less than 14.7psi -- Denver is at a
bit over 12psi and Santa Fe is at about 11 -- but that doesn't seem to
have been seriously considered...
--
Committees do harm merely by existing.             |       Henry Spencer
                           -- Freeman Dyson        |   henry@zoo.toronto.edu

From: gherbert@crl3.crl.com (George Herbert)
Newsgroups: sci.space.policy
Subject: Re: Space "Capsule" Space Suits... a possible alternative?
Date: 20 Jan 2000 13:13:34 -0800

Henry Spencer <henry@spsystems.net> wrote:
>In many ways, it would make sense to run the cabin at somewhat lower
>pressure.  But there are disadvantages, particularly for life-sciences
>work where you want to run control experiments on the ground (because
>those control experiments then need to be done in low-pressure chambers to
>ensure that the results aren't messed up by differences in atmosphere).

I personally think there's plenty of justification for a NASA
or university reduced pressure research facility in Vail, Colorado.
And/or a lot of reduced pressure research labs at existing facilities.
And/or mixed buffer gas labs as well.

The advantages of a 12 PSI, 9+3 atmosphere are obvious (no prebreathe
to 8 PSI suit, and about half existing prebreathe times for 4.5 PSI).
I've seen credible arguments for as low as 10 PSI habitats (7.5/2.5
or 7/3).  If your limiting bends ratio (ppN2/ppFinal) for no prebreathe
is 1.3, then you can't quite do a zero prebreathe 4 PSI suit without
going to a mix with oxygen/helium/nitrogen or oxygen/helium/argon/nitrogen
assuming flammability concerns for the hab are properly paid attention to.
You can't use too much helium or communications gets wierd, you need
denser gases but not too much nitrogen.  I've always been curious about
a 3/3/3/3 mixture of the O2/He/Ar/N mix.  But you want a bunch of biomedical
research (including running some bed rest studies in it, animal studies,
etc etc) prior to flying anything.

And no, I don't ski at all, so I'm not trying to sneak in a
R&R program for space researchers 8-)


-george william herbert
gherbert@crl.com

From: gherbert@crl3.crl.com (George Herbert)
Newsgroups: sci.space.policy
Subject: Re: Space "Capsule" Space Suits... a possible alternative?
Date: 20 Jan 2000 15:47:21 -0800

Rand Simberg <simberg.interglobal@trash.org> wrote:
>gherbert@crl3.crl.com (George Herbert) made the phosphor on my monitor
>glow in such a way as to indicate that:
>>The advantages of a 12 PSI, 9+3 atmosphere are obvious (no prebreathe
>>to 8 PSI suit, and about half existing prebreathe times for 4.5 PSI).
>>I've seen credible arguments for as low as 10 PSI habitats (7.5/2.5
>>or 7/3).  If your limiting bends ratio (ppN2/ppFinal) for no prebreathe
>>is 1.3, then you can't quite do a zero prebreathe 4 PSI suit without
>>going to a mix with oxygen/helium/nitrogen or oxygen/helium/argon/nitrogen
>>assuming flammability concerns for the hab are properly paid attention to.
>>You can't use too much helium or communications gets wierd, you need
>>denser gases but not too much nitrogen.  I've always been curious about
>>a 3/3/3/3 mixture of the O2/He/Ar/N mix.  But you want a bunch of biomedical
>>research (including running some bed rest studies in it, animal studies,
>>etc etc) prior to flying anything.
>
>Are those NASA specs?  The last time I looked at them (which was
>admittedly almost two decades ago) the source seemed to be Navy dive
>tables.  IOW, they were extrapolating hyperbaric data to a hypobaric
>situation, because they didn't have much of a data base for hypobaric.
>I've always questioned the validity of that, and I still think that
>they're rolling the dice to some degree with EVAs even with
>prebreathing.  I've heard rumors that some astronauts have in fact
>gotten bent, but not ever been able to confirm them...

NASA doesn't have a hard firm spec applicable to zero prebreathe
that I know of, if you do prebreathe then it's nontrivial to compare
to a zero prebreathe system.

They do have a fair amount of data on hypobarics from NASA testing,
and some from on orbit activities (US and Russian).  The Russians
run a lot closer to getting bent, but they rigorously preselect for
cosmonauts not very susceptable to getting bent (you can apparently
screen it pretty well, and they push past bends ratio of 1.6 I think).

Somewhere between 1.2 and 1.3 is probably the safe limit for no more
than minimal effects for even average susceptability persons at no
prebreathe.  I personally think that if you're going to a 3-gas mix
or more, you might as well do it enough that you get a bends ratio
of 1.1 or lower.  Between communications and biomedical issues,
I suspect there's a sweet spot with 3/3/3/3 or 2.5/2.5/2.5/2.5
using O/He/Ar/N, in terms of bends, fire risk, communications,
and station design issues.  This may take some time and experimentation
to properly analyze, but is something which would really improve
our ability to live in space in the long term.


-george william herbert
gherbert@crl.com

Newsgroups: sci.space.policy
From: henry@spsystems.net (Henry Spencer)
Subject: Re: Space "Capsule" Space Suits... a possible alternative?
Date: Fri, 21 Jan 2000 04:48:59 GMT

In article <3887BB06.1C29C318@qnet.com>, Doug Jones  <random@qnet.com> wrote:
>George Herbert wrote:
>> I personally think there's plenty of justification for a NASA
>> or university reduced pressure research facility in Vail, Colorado.
>
>Cripple Creek is higher, at 10,000 feet...

In practice, I think about 8,000ft is the "sweet spot" for reduced
pressure.  It's enough to make a difference but not enough to cause real
problems.  In particular, almost all standard air-cooled electronics gear
is rated to work at that altitude, but *not* a lot higher.  Most people
also find it relatively easy to adapt, which again is not true if you go
much higher.

I forget how high up Vail is.  Santa Fe is at about 8000ft.

>Aha! Mauna Kea- 13,796 feet, better weather than Colorado, good road kept
>open for the observatories, and the beach is only two hours drive away :)

Unfortunately, Mauna Kea is high enough that people do have serious
altitude problems.  Especially if they go down and hit the beach after
work. :-)
--
The space program reminds me        |  Henry Spencer   henry@spsystems.net
of a government agency.  -Jim Baen  |      (aka henry@zoo.toronto.edu)

Date: Thu, 20 Jan 2000 23:57:23 -0800
From: Doug Jones <random@qnet.com>
Newsgroups: sci.space.policy
Subject: Re: Space "Capsule" Space Suits... a possible alternative?

Henry Spencer wrote:
>
> Doug Jones  <random@qnet.com> wrote:
>
> >Aha! Mauna Kea- 13,796 feet, better weather than Colorado, good road kept
> >open for the observatories, and the beach is only two hours drive away :)
>
> Unfortunately, Mauna Kea is high enough that people do have serious
> altitude problems.  Especially if they go down and hit the beach after
> work. :-)

Yeah, I remember seeing some *very* altitude-sick locals at about 10,000
feet when I hitchhiked up there in 1980- they boggled to see someone
briskly walking up the mountain road... not everyone has the advantage of
living above 6,000 feet for years.

Then there's the tech support camp for the observatories at 9,000 feet-
it's probably easier to set up a facility there than at the summit
anyway... and Hawaii has the advantage that a sea level control lab could
be nearby.

Actually, the cheapest way to study high altitude acclimation in the US
would be to pick a spot in Colorado- oh well.

--
Doug Jones
Rocket Plumber, XCOR Aerospace
http://www.xcor-aerospace.com

From: gherbert@crl3.crl.com (George Herbert)
Newsgroups: sci.space.policy
Subject: Re: Space "Capsule" Space Suits... a possible alternative?
Date: 22 Jan 2000 00:20:19 -0800

Filip De Vos <fidevos@eduserv1.rug.ac.be> wrote:
>Rand Simberg (simberg.interglobal@trash.org) wrote:
>: <gbaikie@hotmail.com> wrote:
>: >Why do you need 15 psi? Why not a lower pressure? I believe that at or
>: >above 45,000' elevation pressure you need a pressure suit to breath.
>: >Why not use the psi of around 25,000' or around 8 psi.
>
>: 8 psi is fine if your habitat is at that pressure, but if you're
>: leaving from a one-atmosphere airlock, you need to prebreathe O2 for
>: several hours to reduce risk of the bends.  High-pressure suits will
>: improve productivity and make EVA much more routine.
>
>Professional vac-workers will prefer to live in a third-of-an-atmosphere
>(or less) of pure oxygen, eliminating pre-breathing and risk of the
>bends...

Professional vac workers will want to be able to have comfortable
throats and avoid lung problems which come with 5 PSI or less pure O2.

There's no reason to completely avoid mixed gases.  The issues are
clear: the bends, which is avoided by keeping ppN2hab/suitpress to
no more than 1.2 to 1.3, suit mobility which argues for minimal suitpress,
minimum lung water boiling pressure pushing for not much less than 4
PSI in the lung, user comfort in the hab and in the suit, enough ppO2
in the hab and in the suit, etc etc.

All things considered, 5 PSI O2 is too much of a fire hazard and is
too hard on people's throats and lungs for a permanent hab.
It won't kill you, but spending millions of dollars to fly
an astronaut and then provide him with an irritating environment
which will degrade his physical performance seems to be muchly
foolish to me.  The fire danger might kill you, and a lot of things
burn in 5 PSI O2 which you wouldn't think burn well so designing
around it materials-wise gets reaaalllyyy tricky, probably nearly
impossible.  Not flash fire critical like 1 atm O2 but it's still
much more dangerous.

There are other buffer gases which help balance out the concerns.
Helium, although it introduces a slight communications problem, is great.
Argon is ok.  Nitrogen (with the bends ratio taken into account) is ok.
So something like 3/3/3/3 or 2.5/2.5/2.5/2.5 should do fine.
Variants on these (I've seen O/He/Ar/N of 4/2/2/4 before) work as well.
The question of what's "right" is a good one, but I suspect will be
something more like this than pure O2 at 1/3 atm or so.


-george william herbert
gherbert@crl.com

Newsgroups: sci.space.policy
From: henry@spsystems.net (Henry Spencer)
Subject: Re: Pure Oxygen atmosphere
Date: Sat, 22 Jan 2000 20:27:08 GMT

In article <869vlu$5ka$1@nnrp1.deja.com>,
Len (Cormier) for MMI  <len@tour2space.com> wrote:
>I have been under the (perhaps mistaken) impression
>that 3 psi pure oxygen is no more dangerous than a
>normal partial pressure of 3 psi oxygen in a 14.7
>psi atmosphere...

Not so, alas.  Two things matter:  how much oxygen there is in the
atmosphere, and how effectively it removes heat from the flame.  The
oxygen partial pressure pretty much determines the former.  However, inert
diluent gases have a big effect on the latter.

So no, 3psi pure oxygen is much more dangerous than 14.7psi air, because
flames hold heat better in the thin atmosphere.  At the other extreme,
it's quite possible to devise a breathable atmosphere which will not
support a flame at all, although the pressure has to be rather higher than
Earth-surface.

The fire-code rule (unless it's been changed recently, my reference is a
bit old) is that if the percentage of oxygen exceeds 23.45/sqrt(atm),
where atm is the total pressure in atmospheres, that is an "atmosphere
of increased burning rate".
--
The space program reminds me        |  Henry Spencer   henry@spsystems.net
of a government agency.  -Jim Baen  |      (aka henry@zoo.toronto.edu)

From: gherbert@crl3.crl.com (George Herbert)
Newsgroups: sci.space.policy
Subject: Re: Space "Capsule" Space Suits... a possible alternative?
Date: 22 Jan 2000 17:55:46 -0800

Henry Spencer <henry@spsystems.net> wrote:
>Jonathan A Goff  <jongoff@et.byu.edu> wrote:
>>Interesting thought, would adding more massive particles like say
>>Xenon to the spacesuit allow for safer usage (by having more thermal
>>mass per psi of pressure), or are there too many drawbacks.
>
>Alas, there are drawbacks.  Xenon is an anesthetic.  14.7psi with all the
>nitrogen replaced by xenon will knock you out quite nicely; it would be
>used as a surgical anesthetic if xenon wasn't so expensive.  (Granted, you
>can recover it, but that's a technical headache.)  Smaller amounts tend to
>make you drunk.
>Nitrogen will do the same things, actually, but only at higher pressure.

So will helium at high enough pressure.  That's why really really deep
divers use hydrogen oxygen mixtures; helium narcosis eventually becomes
a terrible problem.

Argon isn't nearly as anesthetic as xenon is.  It's worse than nitrogen
is for anesthetic effects but doesn't risk the bends nearly as much.
That's why I think that an oxygen/helium/argon/nitrogen mix is likely
where the best balance point is.  With 3 PSI of each and a 4 PSI
pure oxygen suit, the bends ratio for nitrogen alone is only 0.75,
and given argon's contribution it's around 1.2 or so based on what
info is available now (needs to be restudied in depth, I think).
The helium content won't be high enough to wreck communications,
the ppO2 is only 25% of the total gas mix, which given that the
total pressure is only 0.8 bar gives an adequately non-fire-enhancing
atmosphere.


-george william herbert
gherbert@crl.com

Newsgroups: sci.space.policy
From: henry@spsystems.net (Henry Spencer)
Subject: Re: Space "Capsule" Space Suits... a possible alternative?
Date: Sun, 23 Jan 2000 04:26:48 GMT

In article <86da85$fe0$1@nnrp1.deja.com>, gbaikie  <gbaikie@hotmail.com> wrote:
>> ...conditions which didn't qualify as an "atmosphere of
>> increasing burning rate" by industrial fire-safety rules.  You can't go
>> below 10-12psi (depending on how fussy you are about oxygen content :-))
>> and still evade that.
>
>Are fires were a problem on mountains 12,000' (about 9.4 psi) or higher?

No, but oxygen shortage is.  Pilots flying at a (cabin) altitude of
12500ft or higher are legally required to use oxygen masks, and in fact
smart pilots start using oxygen considerably below that, because it makes
a real difference to mental processes.
--
The space program reminds me        |  Henry Spencer   henry@spsystems.net
of a government agency.  -Jim Baen  |      (aka henry@zoo.toronto.edu)

Newsgroups: sci.space.policy
From: henry@spsystems.net (Henry Spencer)
Subject: Re: Space "Capsule" Space Suits... a possible alternative?
Date: Sun, 23 Jan 2000 18:56:18 GMT

In article <86e02v$49n$1@inf6serv.rug.ac.be>,
Filip De Vos <fidevos@eduserv1.rug.ac.be> wrote:
>: Professional vac workers will want to be able to have comfortable
>: throats and avoid lung problems which come with 5 PSI or less pure O2.
>                    ^^^^^^^^^^^^^
>IIRC, the Skylab astronauts did (like all American astronauts until then)
>use pure O2 at 1/3atm (*). I did not know wether they had lung/throat
>problems...

Skylab did not use pure O2 -- it ran at 5psi with about 75% oxygen and 25%
nitrogen.  Also, there was some reduction of lung capacity observed in
some of the Skylab astronauts, although it was mild and vanished quickly
after return.
--
The space program reminds me        |  Henry Spencer   henry@spsystems.net
of a government agency.  -Jim Baen  |      (aka henry@zoo.toronto.edu)

From: gherbert@crl3.crl.com (George Herbert)
Newsgroups: sci.space.policy
Subject: Re: Space "Capsule" Space Suits... a possible alternative?
Date: 23 Jan 2000 18:04:06 -0800

Jonathan A Goff  <jongoff@et.byu.edu> wrote:
>On Sun, 23 Jan 2000, Henry Spencer wrote:
>> Skylab did not use pure O2 -- it ran at 5psi with about 75% oxygen and 25%
>> nitrogen.  Also, there was some reduction of lung capacity observed in
>> some of the Skylab astronauts, although it was mild and vanished quickly
>> after return.
>
>75% O2 isn't a safe mix is it?

No, the maximum ppO2 for 5 PSI which is still not a fire enhancing
atmosphere is 2 PSI.  3.75 PSI ppO2 is clearly combustion enhancing.


-george william herbert
gherbert@crl.com

Newsgroups: sci.space.policy
From: henry@spsystems.net (Henry Spencer)
Subject: Re: Pure Oxygen atmosphere
Date: Wed, 9 Feb 2000 06:28:04 GMT

In article <2C5o4.1348$v74.21789@ord-read.news.verio.net>,
Bloody Viking  <nospam@masu.wwa.com> wrote:
>: ...At the other extreme,
>: it's quite possible to devise a breathable atmosphere which will not
>: support a flame at all, although the pressure has to be rather higher than
>: Earth-surface.
>
>At what pressure would this fire-safe "air" be? I suppose it would use
>helium as the diluent, as helium carries away heat real good. But a side
>effect is that such "air" would make the people in it sound like Michael
>Jackson.

I think you can do it with nitrogen, although you'd need at least a few
atm. of total pressure and a corresponding reduction of oxygen content,
I'd guess.  (You want to maintain the same oxygen partial pressure, not
the same oxygen fraction.)  I'm not sure I've ever seen exact numbers.
--
The space program reminds me        |  Henry Spencer   henry@spsystems.net
of a government agency.  -Jim Baen  |      (aka henry@zoo.toronto.edu)

Newsgroups: sci.space.policy
From: henry@spsystems.net (Henry Spencer)
Subject: Re: Pure Oxygen atmosphere
Date: Wed, 9 Feb 2000 16:49:30 GMT

In article <SVdo4.1412$v74.22928@ord-read.news.verio.net>,
Bloody Viking  <nospam@miles.wwa.com> wrote:
>: I think you can do it with nitrogen, although you'd need at least a few
>: atm. of total pressure and a corresponding reduction of oxygen content,
>: I'd guess...
>
>You can't get too carried away using nitrogen. At enough pressure,
>nitrogen becomes an anesthetic like laughing gas. (:

True, there are limits to what you can do with nitrogen.
--
The space program reminds me        |  Henry Spencer   henry@spsystems.net
of a government agency.  -Jim Baen  |      (aka henry@zoo.toronto.edu)

Newsgroups: sci.space.policy
From: henry@spsystems.net (Henry Spencer)
Subject: Re: Pure Oxygen atmosphere
Date: Thu, 10 Feb 2000 20:22:18 GMT

In article <38A20F76.BD330DF0@mail.com>, Bill Bonde  <stderr@mail.com> wrote:
>> : I think you can do it with nitrogen, although you'd need at least a few
>> : atm. of total pressure and a corresponding reduction of oxygen...
>> You can't get too carried away using nitrogen. At enough pressure,
>> nitrogen becomes an anesthetic like laughing gas. ...
>
>Do you think you would have to get to that high of a pressure before you
>created an environment that couldn't support flame?

Yup.  Right after saying that I'd never seen precise numbers, I ran across
some.  Sealab II, one of the 1960s living-underwater experiments, ran at
7atm total pressure with 4% oxygen, a slightly higher oxygen partial
pressure than sea level.  The smokers aboard it were deeply unhappy about
this:  never mind cigarettes, their *matches* wouldn't ignite.
--
The space program reminds me        |  Henry Spencer   henry@spsystems.net
of a government agency.  -Jim Baen  |      (aka henry@zoo.toronto.edu)

Date: Fri, 11 Feb 2000 15:50:56 -0800
From: Doug Jones <random@qnet.com>
Newsgroups: sci.space.policy
Subject: Re: Pure Oxygen atmosphere

Henry Spencer wrote:
>
> I wrote:
> >>> You can't get too carried away using nitrogen. At enough pressure,
> >>> nitrogen becomes an anesthetic like laughing gas. ...
> >>Do you think you would have to get to that high of a pressure before you
> >>created an environment that couldn't support flame?
> >
> >Yup. Right after saying that I'd never seen precise numbers, I ran
> >across some.  Sealab II, one of the 1960s living-underwater experiments,
> >ran at 7atm total pressure with 4% oxygen, a slightly higher oxygen
> >partial pressure than sea level.  The smokers aboard it were deeply
> >unhappy about this:  never mind cigarettes, their *matches* wouldn't
> >ignite.
>
> Oops; obviously that should have been "Nope.", as per the commentary
> that followed!

Hey, I think I have an "I corrected Henry Spencer" winner here- 7
atmospheres absolute pressure is the equivalent of 180 feet of sea
water, definately in the narcosis danger area. From
http://www.mtsinai.org/pulmonary/books/scuba/gaspress.htm:

   Nitrogen narcosis, also called "rapture of the deep" and "the martini
   effect," results from a direct toxic effect of high nitrogen pressure on
   nerve conduction. It is an alcohol-like effect, a feeling often
   compared to drinking a martini on an empty stomach: slightly giddy,
   woozy, a little off balance.

   Nitrogen narcosis is a highly variable sensation but always
   depth-related. Some divers experience no narcotic effect at depths
   up to 130 fsw, whereas others feel some effect at around 80 fsw.
   One thing is certain: once begun, the narcotic effect increases with
   increasing depth. Each additional 50 feet depth is said to feel like
   having another martini.

The Sealab experiments must have included a large fraction of helium to
prevent narcosis, so indeed, to get a non flame-supporting atmosphere
with nitrogen, you have to go to narcotic pressures.

On further thought, the Sealab data point merely shows that a breathable
mix at 7 bar must have helium, it doesn't show that a nitrox mixture at
lower pressure can't be flameproof and nonnarcotic- although the data
hints at it, I don't have a reference.  Yet.

Damn, Henry, you're slippery.

--
Doug Jones
Rocket Plumber, XCOR Aerospace
http://www.xcor-aerospace.com

Newsgroups: sci.space.policy
From: henry@spsystems.net (Henry Spencer)
Subject: Re: Pure Oxygen atmosphere
Date: Sat, 19 Feb 2000 18:49:07 GMT

In article <38A4A060.19606196@qnet.com>, Doug Jones  <random@qnet.com> wrote:
>> >...Right after saying that I'd never seen precise numbers, I ran
>> >across some.  Sealab II, one of the 1960s living-underwater experiments,
>> >ran at 7atm total pressure with 4% oxygen, a slightly higher oxygen
>> >partial pressure than sea level...
>
>Hey, I think I have an "I corrected Henry Spencer" winner here- 7
>atmospheres absolute pressure is the equivalent of 180 feet of sea
>water, definately in the narcosis danger area...
>The Sealab experiments must have included a large fraction of helium to
>prevent narcosis, so indeed, to get a non flame-supporting atmosphere
>with nitrogen, you have to go to narcotic pressures.

On looking more closely at the stuff I was reading, although it vaguely
implies that nitrogen was used, it doesn't actually *say* what the buffer
gas was.  A bit of digging indicates that the Sealab buffer gas was likely
mostly or entirely helium.  (I don't have the right references to be sure.)

>On further thought, the Sealab data point merely shows that a breathable
>mix at 7 bar must have helium, it doesn't show that a nitrox mixture at
>lower pressure can't be flameproof and nonnarcotic...

True.  Although, the same document I was reading does have some discussion
of using higher nitrogen pressure to reduce fire hazard, and it's quite
definitely talking in terms of *reducing* it rather than eliminating it,
which suggests that elimination isn't in fact practical with nitrogen.
--
The space program reminds me        |  Henry Spencer   henry@spsystems.net
of a government agency.  -Jim Baen  |      (aka henry@zoo.toronto.edu)

Newsgroups: sci.space.policy
From: henry@spsystems.net (Henry Spencer)
Subject: Re: Pure Oxygen atmosphere
Date: Sat, 19 Feb 2000 18:52:42 GMT

In article <950310208.22088.0.nnrp-08.9e98d142@news.demon.co.uk>,
Ian Stirling  <Inquisitor@I.am> wrote:
>>...Sealab II, one of the 1960s living-underwater experiments, ran at
>>7atm total pressure with 4% oxygen, a slightly higher oxygen partial
>>pressure than sea level.  The smokers aboard it were deeply unhappy about
>>this:  never mind cigarettes, their *matches* wouldn't ignite.
>
>Do you perhaps mean that the match stem won't burn?
>I'm pretty sure that the pyrotechnic compound on the tip wouldn't be
>that affected by pressure.

I was surprised too, but they definitely said that the matches simply
wouldn't work at all.  Mind you, this was not a primary source -- it was a
paper on fire hazards mentioning Sealab experience, rather than a paper on
Sealab -- so it may be wrong.  On the other hand, the author seems to have
been at NRL doing work on submarine fire prevention, so he'd be in a good
position to know the details.
--
The space program reminds me        |  Henry Spencer   henry@spsystems.net
of a government agency.  -Jim Baen  |      (aka henry@zoo.toronto.edu)

Newsgroups: sci.space.policy
From: henry@spsystems.net (Henry Spencer)
Subject: Re: Terraforming Venus
Date: Fri, 7 Jul 2000 11:45:11 GMT

In article <Pine.GHP.4.21.0007062118320.5928-100000@cancer.et.byu.edu>,
Jonathan A Goff  <jongoff@et.byu.edu> wrote:
>Just wondering, but even with the right mix, would someone
>even be able to breath in a 90 bar atmosphere?

Yes, it's been done experimentally in pressure chambers -- research for
very-deep-diving work.  I don't think anyone has actually gone that far
down in real water, though.

The muscular effort of breathing becomes a non-trivial issue at such
pressures.
--
Microsoft shouldn't be broken up.       |  Henry Spencer   henry@spsystems.net
It should be shut down.  -- Phil Agre   |      (aka henry@zoo.toronto.edu)

Newsgroups: sci.space.policy
From: henry@spsystems.net (Henry Spencer)
Subject: Re: Terraforming Venus
Date: Fri, 7 Jul 2000 20:48:58 GMT

In article <396629E0.28EBBF5B@mail.com>, Bill Bonde  <stderr@mail.com> wrote:
>> >even be able to breath in a 90 bar atmosphere?
>> Yes, it's been done experimentally in pressure chambers -- research for
>> very-deep-diving work.  I don't think anyone has actually gone that far
>> down in real water, though...
>
>Isn't that something like 3000 feet?

Somewhere around there.  If memory serves, the chamber work was thought to
indicate that diving to circa 5000ft would be practical with hydrogen,
although I'm not sure whether they actually went to that pressure or just
got results that they thought could be extrapolated to it.
--
Microsoft shouldn't be broken up.       |  Henry Spencer   henry@spsystems.net
It should be shut down.  -- Phil Agre   |      (aka henry@zoo.toronto.edu)

Newsgroups: sci.space.tech
From: henry@spsystems.net (Henry Spencer)
Subject: Re: Atmospheric partial pressure of oxygen
Date: Sun, 17 Dec 2000 03:26:42 GMT

In article <3A3BD707.A1E512EC@indra.com>,
Charles R Martin  <crmartin@indra.com> wrote:
>.. but sitting right where I am now, the actual atmospheric pressure is about
>10.5 lbs/in^2 (6Kft altitude).  19 % of that is about 2 lbs/in^2, so that
>*ought* to be the partial presssure of oxygen ... but appears that NASA shoots
>for more like 5 lbs/in^2.  Why?

Minor nitpick:  oxygen is 21%, not 19%, of air.

More substantively...  There is a serious nonlinearity here.  Air going
into the lungs is diluted by CO2 and water vapor coming out, and that
dilution is by roughly a constant absolute amount, *not* a constant
percentage.  So lower pressures get diluted more, and maintaining the same
oxygen partial pressure *at the lung wall* requires a higher partial
pressure of oxygen in the gas mixture at lower total pressure.

>Similarly, why do they seem to want sea-level pressure when about 2/3 of that
>seems perfectly adequate?

Now *that* is an excellent question, one that others have commented on in
the past.
--
When failure is not an option, success  |  Henry Spencer   henry@spsystems.net
can get expensive.   -- Peter Stibrany  |      (aka henry@zoo.toronto.edu)