Quote:
Originally Posted by wes
I was wondering if anyone has expericence (that they are willing to share) of actually freediving to some depths beyond the accepted safe depth limit (of continuous breathing) with pure O2 or for that matter other mixed gases.
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The toxicity of O2 is influenced by two principal factors: the time you breath the gas, and the partial O2 pressure (combination of percentage of O2 in the gas mixture you breath - in case of pure O2 it is equal to the environmental pressure). You will find tables showing times for which you can breath O2 at different depth in many sources. Check out for example WikiPedia:
Oxygen toxicity - Wikipedia, the free encyclopedia
Maximum operating depth - Wikipedia, the free encyclopedia
The second link shows for example that you could breath pure oxygen for 45min in the depth of 6m, while you could breath safely pure air (~21% of O2) at the dept of 66m for the same time (45min). Apnea times are much shorter (even if on pure O2), so you could afford going deeper - that's why freedivers can go far below the depth that may be already toxic for scuba.
Additionally, the toxicity of O2 due to hyperoxia is reduced by the consumption of O2 in the tissue during apnea, so the tables would be different for apnea (but I doubt you'll find any more precise data anywhere). As already told by others, at apnea on O2, the CO2 toxicity may be often setting on before the O2 toxicity.
