[manhattanguy]

I don’t think that by breathing pure O2 above or on surface will expose you to the risk of any oxygen poisoning. However, there are some risks (including poisoning) involved in diving with pure O2.

I am a member of a combat diving unit (military) and we use the old closed Dräger Lar system. Every year we intensively dive for about two months to maintain our skills in under-water navigation, diving etc. During those two months I log about 350-400 hours of time under water with pure O2 (2 hours morning, 2 afternoon and 2-3 night). Our depth is dependent on water visibility but we try to stay at about 6 meters depth. We do however go deeper if needed but not deeper then about 12 meters. It’s pretty impossible to maintain a depth above 3-4 meters since you run the risk of “popping” up to the surface, that’s because we cannot empty our rebreathers in any other way then by actually breathing up the oxygen in it.

Safety wise, we all go through the “poisoning test” which is to equip the O2 gear, oxygenize the entire body by running 3km and then pressurize in a chamber to 15 meters for 15 minutes. During the years we have not got any O2 poisoning cases. Not even when my buddy’s suit got filled with water and he disappeared down to 24 meters pulling me with him to about 20 before he activated his jacket. We do get a few CO2 pass-outs due to the filter substance being clogged up by water therefore not filtering properly. TRUX is completely right in that pure O2 accelerates aging, and can destroy tissue (I am 35 but look like 50…lol..) but on top of that it completely destroys your physical fitness (your body gets used to pure O2) and that’s why we only do it for 2 months/year. After that you can barley walk up the stairs without frequent breaks.