Oxygen on surface

[TicDiver]

Hello, question for the people who are trained to dive with 100% oxygen.
Do you use oxygen on the surface before the actual dive to preventively reduce nitrogen tissue saturation?
Do you use oxygen after the dive in addition to regular decompression, e.g. on a liveaboard?

 

[J-Vo]

Pre dive O2 is prohibitive as the low pressure gradients would require a long time to make a difference.

I'll do post dive O2 if I feel the decompression was inefficient for some reason or if I have a short time to an ascent to altitude/flying.

BTW: You don't need to be trained to breath O2 on the surface.

 

[justinthedeeps]

Pre-breathing oxygen won't have any effect, since the ppN2 at ambient surface pressure is negligible for SCUBA concerns. It is only the inert gas absorbed while diving at super-atmospheric pressures that matters.

Post-dive 'surface decompression' on oxygen is commonly done, yes. Not sure who (if anyone) does any maths about it. It could be useful for repetitive decompression diving scenarios. Do any dive planners try to model this re: residual inert gases during intervals?

 

[J-Vo]

Subsurface will model surface O2.

Up to a ~50 minute pre breath it shows a 3 minute increase in NDL at 100'. That stays same up to about ~200 minutes, after that it starts to reduce NDL. I'm not sure what is up with the model there.

 

[nadwidny]

Hello, question for the people who are trained to dive with 100% oxygen.
Do you use oxygen on the surface before the actual dive to preventively reduce nitrogen tissue saturation?
Do you use oxygen after the dive in addition to regular decompression, e.g. on a liveaboard?

No.

I don't and I don't see it done by others, except one guy that I dive with and he only does it once in a while.

 

[Capt Jim Wyatt]

I do not do it. Never have. Never did it as a Navy diver. I know of no one who does it for scuba.

 

[boulderjohn]

Like J-Vo in post #2, I only do it after a dive when I am traveling to a higher altitude after the dive. In that case, I not only do it prior to traveling, I do it while traveling. NOAA used to have a table for this, telling how surface breathing of oxygen impacted their dive tables and their ascent to altitude tables.

 

[grantmac]

Better to learn enriched gas deco and hang out for another few minutes at 6m on O2 even after your obligation clears.

 

[LFMarm]

I prefer to stay on O2 (or high pO2 when in CC) in the water after clearing all my deco obligations unless it’s in nasty conditions (e.g., low viz, cold, strong current). Good opportunity to do drills or practice skills. Once SurfGF gets to <30, I believe there is very little need for additional O2 after surfacing.

 

[inquis]

Subsurface will model surface O2.

Up to a ~50 minute pre breath it shows a 3 minute increase in NDL at 100'. That stays same up to about ~200 minutes, after that it starts to reduce NDL. I'm not sure what is up with the model there.

@J-Vo, I believe that's due to an assumed limit in the NDL planner.

Doing the pre-breath at 3 ft (same gradient, but I've noticed issues with depths less than 3 ft before), I get that 19 minute NDL (3-minute increase at GF x/85) from a pre-breath from 17 mins up to a 340 minutes. The planner extends the runtime until 359 minutes, which is a rather suspicious number. Increasing the pre-breath further keeps the runtime at 359 mins using the NDL planner. However, if you directly specify the 19 minute bottom time using the normal planning mode (Buhlmann Deco rather than Recreational mode), the surfacing GF stays just under GFHigh as you'd expect, even for pre-breath times out to 1000 mins (didn't check further).

@TicDiver, in short, there's no gain past a 17 minute pre-breath, and even that is pretty small for your trouble. It's much easier to just shallow up slightly -- the normal NDL is the same when 8 ft shallower compared to the 100 ft pre-breathed NDL. If you want to stay longer than NDL, look into additional training to move beyond recreational limits (both depth and/or time).