100% oxygen, safety stop depth & off gassing

[iainwilliams]

Hello,

I often breath 100% oxygen at 5m (20 feet PPO2 1.5) to enhance offgassing. My hang time at 5 m is usually 5 minutes and I then proceed to 3 m (10 feet) an do an additional 2 to 3 minutes before surfacing. This is not decompression, but rather safety stops from no decompression dive.

My question: Is there much beneifit in the 3 m (10 feet) hang considering the 100% oxygen would be creating a very large pressure gradient for elliminating nitrogen??

There probably is not much data on this - I don't know. I guess I'm curious as to the benifit/ lowering of DCS risk with the addition of the 3 m hang in comparison to doing only a 5 m hang. Is the 3 m hang really helping to ellimate the nitrogen or is it just marginal in its beneifit?

Perhaps it is better to only to the 5 m stop then surface?

As always - thank you................Iain

 

[Rick Inman]

I'm just curious, is the oxygen tank on a line, or are you carrying it with you?

 

[pipedope]

There is probably some benefit to stopping at both 20 and 10' (metric impaired American ) but even more from coming up very slowly that last 10'.

 

[gkndivebum]

There is probably some benefit to stopping at both 20 and 10' (metric impaired American ) but even more from coming up very slowly that last 10'.

Indeed. Our SOP for decompression diving calls for a 10 minute ascent from 20 FSW
after we've finished our deco at that stop.

The last 4 feet can be a pain ....

 

[MechDiver]

Hello,

I often breath 100% oxygen at 5m (20 feet PPO2 1.5) to enhance offgassing. My hang time at 5 m is usually 5 minutes and I then proceed to 3 m (10 feet) an do an additional 2 to 3 minutes before surfacing. This is not decompression, but rather safety stops from no decompression dive.

As 5 minutes at 20 feet on O2 (1.6 ppo2 BTW) for a safety stop from an NDL dive is total overkill to begin with, I would see absolutely no reason to do additional stops.

Have you been trained to use O2?

 

[iainwilliams]

As 5 minutes at 20 feet on O2 (1.6 ppo2 BTW) for a safety stop from an NDL dive is total overkill to begin with, I would see absolutely no reason to do additional stops.

Have you been trained to use O2?

Mech Diver: Yes 1.6 PPO2 at 20 feet quite right - I use metric not imperial and usually do 5 m at PPO2 at 1.5. Yes I have trained with Oxygen to answer your question, but little was said during my course outlining the answer to my question - thanks for your imput..........Iain

 

[iainwilliams]

I'm just curious, is the oxygen tank on a line, or are you carrying it with you?

I normally use a 20 cu pony which I take with me........Iain

 

[iainwilliams]

Thanks to all that answered.............Iain

 

[Dr Deco]

Many thanks to the responders. I did not have any quantitative info on this topic.

Dr D.

Readers, please note the next class in Decompression Physiology :1book:
http://wrigley.usc.edu/hyperbaric/advdeco.htm

 

[DepartureDiver]

From a decompression perspective, there is an advantage at staying deeper (ignoring vasoconstriction) at 5m (16') since bubbles will be kept smaller. This is NOT an oxygen window benefit since this term is often misunderstood and used incorrectly. This is because the bubble skin pressure on smaller bubbles is greater which helps with gas elimination. However, as others have stated, there is also a good benefit to coming up very slow. So the 3 m. stop can assist greatly with that by forcing a very slow ascent. Since you are not doing any dives requiring a true ceiling, I think the 3 m. stop for you is beneficial. But don't forget some nice deep safety stops on the way to your 5 m. stop.