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'[OT] ph and CO2 measurers?'
1998\03\26@000341 by Mike Keitz

picon face
On Wed, 25 Mar 1998 10:10:56 -0700 Justin Crooks <spam_OUTjcrooksTakeThisOuTspamWYOMING.COM>
writes:
>I have seen studies where up to 35% CO2 was mixed with sufficient
>oxygen,
>and breathed comfortably for quite some time.  I think the only danger
>of
>CO2 is that it typically is the byproduct of an oxygen-consuming
>reaction,
>and therefore there is insufficient oxygen to sustain consciousness
>(and/or
>life).

If you could quote those studies, it would be more believable.  I did a
little research, and found that information on C02 is rather scarce in
the industrial hygiene literature, probably because C02 poisoning is not
a major problem.  According to the Conference of Governmental Industrial
Hygienists, Inc's 1980 book "Documentation of TLV's" (Threshold Limit
Values ?), a 7-10% concentration of CO2 will cause unconsciousness within
a few minutes, and presumably subsequent death.  This is based on a 1931
German study.  The recommended limit is 0.5% averaged over 8 hours, and
1.5% for short intervals (15 minutes).  Higher limits (up to 5%) are
considered acceptable for people meeting certain medical qualifications.
Perhaps people who are constantly exposed to high concentrations (e.g.
Biosphere 2 residents) would be able to adapt to a 10% concentration.
Spacecraft are designed for about 0.6% or less.

I found no mention of higher than normal O2 concentration providing an
increase in CO2 tolerance.  From the limited physiology that I know, I
would think that the amount of oxygen (as replacement for nitrogen)
combined with the C02 would have little effect.  Two independent types of
perfusion are at work in the lungs.  One perfusion gets oxygen in, and
depends on the oxygen level in the breathed air being sufficiently high.
The other gets C02 out, and depends on the C02 level in the breathed air
being sufficiently low.  Above a certain level, the body is unable to
compensate for the acidity of the blood caused by dissolved C02.

However, perfusion is driven by partial pressures, so an atmosphere of
35% CO2 and 65% O2 may be tolerable if the total pressure is about 1/4 of
normal atmospheric (not likely to happen in the typical basement "farm"
except maybe in case of a tornado).  This would be roughly the same C02
and O2 partial pressures found in normal-pressure air with 8% C02.

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1998\03\26@135721 by Russell McMahon

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I think it's going to be hard to get PICs into this OT subject :-).
Maybe someone is going to propose a partial pressure meter?

Based on what I have read, exposure to high CO2 levels can indeed be
fatal. Most of what was attached sounds rightish.

Based on rather imperfect memories from a book on high altitude and
space medicine that I read a while ago I understand it goes something
like this: The body uses CO2 concentration in a complicated feedback
loop to control what it "thinks" is going on given the range of
conditions which are normally met on earth (ie from sea level to about
25000 feet altitude). The haemoglobin molecule has an interesting
accept /dump oxygen action which when plotted against CO2
concentration (or probably partial pressure) is somewhat S shaped like
a hystreresis  curve. At low CO2 levels oxygen is bound and at high
levels (in the body tissues) it is released. The cross over point
occurs quite rapidly and is controlled by other physiological factors.
High altitude aclimitisation consists of training one's body to
breathe differently which in turn adjusts CO2 levels from where they
would be if you breathed the same as at low altitudes with the result
that the accept/dump point on the hemoglobin curve is moved. A sherpa
typically lives in this mode all the time. A coast dweller taken
straight to 25000+ feet would die of asphyxia but after a slow build
up (over weeks at least) can handle it.

Conclusion: Playing around with the bodies feedback loop can lead to
asphyxia even when there is lots of O2 present. People who know what
they are doing can fool the mechanism to advantage. Your mileage may
vary.

{Just looked for book - can't find it - can dig it up sometime if
anyone is excessively interested}.

 _________________________
|                                                                 |
| - Quantum Mechanics
|   The Dreams that Stuff are made of.
|
| -  All models are wrong -
|   some models are useful.
| _________________________ |

{Original Message removed}

1998\03\27@084550 by Leo van Loon

flavicon
face
This discussion is getting as very [OT] as the question: is water a poison?

Back to the topic: CO2 plays an important role in growing plants in a
greenhouse and must be added just like water and menure.
In the greenhouse nextdoor, they grow Gerbera's, CO2 is monitored and kept
on a level of about 300 PPM by burning natural gas. The CO2 meter is an IR
absorbtion meter with a maximum scale of 3000 PPM.
It needs about a month to stabelize the fist time, and must be calibrated at
least every month with standard mixtures of gas. The whole procedure costs a
few thousand guilders a year, not a problem when you grow a few million
guilders worth of Gerbera's.
I think its a pity, but this type of sensors are of no use for amateurs.
You can use simple glass-chemistry to determine the CO2 content. It costs a
lot of time, but gives also a lot of fun!

-----Oorspronkelijk bericht-----
Van: Mike Keitz <.....mkeitzKILLspamspam@spam@JUNO.COM>
Aan: PICLISTspamKILLspamMITVMA.MIT.EDU <.....PICLISTKILLspamspam.....MITVMA.MIT.EDU>
Datum: donderdag 26 maart 1998 6:17
Onderwerp: Re: [OT] ph and CO2 measurers?


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