O2 diving questions

[Andrew the fish]

freediving on pure O2 questions

heard a few times about taking a breath of O2 before the dive. So, my questions are... many. All the freediving sentimentals aside. Can O2 be used repeatedly? Just for fun I mean. Any burnt throat, lung irritation or watnot? I mean, all dives on O2, or partially enriched air.

I remember something about 20m being an absolute limit for rebreathers, older types that didn't compensate for partial O2 pressure. Is there toxic effects of pure O2 in freediving to such depths?

Another BIG question is - how safe are O2 dives? I know we are talking inherently dangerous thing, but comparatively speaking. Is there much diference in progression of a dive, like contractions, urge to breath, menthal clouding and such? Wouldn't it be anything like euphoric pleasure dive followed by abrupt BO?

 

[trux]

There is already one very similar thread. Although it speaks just about enriched air, most concerns and comments apply also for O2:

http://forums.deeperblue.com/freediving-science/84454-freediving-36-40-o2.html

 

[Jouskari]

Simply put:

Oxygen partial pressure in air at 1 bar = 0,21 right? (21%)

Oxygen partial pressure in 100 % oxygen at 1 bar = 1,0 partial pressure right? (100%)

Oxygen partial pressure in air at 2 bar (10 m depth) = 0,42

Oxygen partial pressure at 2 bar on 100 % oxygen = 2,0

Theoretical limit for O2 poisoning is 1,6. So I would strongly advice against it.

[ame="http://en.wikipedia.org/wiki/Oxygen_toxicity"]Oxygen toxicity - Wikipedia, the free encyclopedia[/ame]

"
Exposures, from minutes to a few hours, to partial pressures of oxygen above 1.6 bars (160 kPa)—about eight times the atmospheric concentration—are usually associated with central nervous system oxygen toxicity and are most likely to occur among patients undergoing hyperbaric oxygen therapy and divers. Since atmospheric pressure is about 1 bar (100 kPa), central nervous system toxicity can only occur under Hyperbaric medicine - Wikipedia, the free encyclopedia conditions, where Ambient pressure - Wikipedia, the free encyclopedia is above normal.Divers breathing air at depths greater than 60 m (200 ft) face an increasing risk of an oxygen toxicity "hit" (seizure). Divers breathing a gas mixture enriched with oxygen, such as Nitrox - Wikipedia, the free encyclopedia, can similarly suffer a seizure at shallower depths, should they descend below the maximum depth allowed for the mixture.
"