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----- From: Mike Keitz To: PICLIST@MITVMA.MIT.EDU Date: Thursday, 26 March 1998 17:12 Subject: Re: [OT] ph and CO2 measurers? >On Wed, 25 Mar 1998 10:10:56 -0700 Justin Crooks >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 ... snip AND > >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. > >_____________________________________________________________________ >You don't need to buy Internet access to use free Internet e-mail. >Get completely free e-mail from Juno at http://www.juno.com >Or call Juno at (800) 654-JUNO [654-5866] >