Posted by CalAbDiver on August 21, 2001 at 15:56:00:
In Reply to: Re: That's FO2 mike posted by nate on August 21, 2001 at 15:25:07:
btw, I am HONORED to be LABELED as a TECH DIVER with the REST OF THE TECH DIVERS !!!
i do not believe i am worthy of that title yet, however, but thank you anyway.
PO2 or ppO2 is "partial pressure" of Oxygen. The United States Navy discovered back in the 1940s and 1950s that divers breathing pure oxygen in their rebreathers and tanks had a tendancy to die.
This soon became attributed to the "double-pure" phenomenon that when pure O2 is breathed at 33 feet of salt water [fsw] that it was a totally unnatural substance, like doubly as "thick" as pure O2 at the surface, due to molecular compression, and therefore death happened for some STILL unknown reason. The turned to college physics and this was then dubbed PARTIAL PRESSURE OF O2 OF 2.0 ATMs [now called ATAs].
That lead to a study as to WHAT is really a dangerous ppO2 [or PO2] level? Today, NOAA and Rodales agree that 1.6 is the maximum safe dosage for oxygen concentration in a gas mix.
There are also gas laws in college physics that explain it:
Boyles Law [B = breathholding is bad, my version]
Charles' Law [C = cold fills are better than hot, my version]
Dalton's Law [D = Deep diving involves partial pressures / P ATA = ppO2 + ppN2 + ppCO2 + etc = 1.0 ATA at mean sea level, 2.0 ATA at 33 fsw, 3.0 at 66 fsw, etc.]
partial pressures are a feature of Daltons Law of physics gas laws.
there is also Henry's Law [H = helium is better for deep diving because ... / pp's of individual gasses will dissolve into blood, tissues, and other liquids in proportion to the solubilities of the individual gasses in the mix and dependent on their partial pressures. this is a ppN2 issue.]
oh yah, almost forgot MHK's little mistake:
P ATA = (D '/. 33 fsw) + 1
where D = depth in feet of sea water (civilians tend to call this "feet of salt water")
ppO2 = [(D '/. 33 fsw)+1] x %O2
where %O2 aka FO2 where F stands for "fraction of O2."
most of that stuff is D/M or tech diver info.
i hope that is as clear as mud, at least. when i dive in mud, i turn on my dive lite.
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