O2 after dive

[Centrals]

Didn't some UWATEC nitrox computers have an error in programming that assumed continued nitrox use on the SI thus reducing the divers apparent nitrogen load? Seems there was a recall over that.

Uwatec was sued by several divers.

 

[lv2dive]

In all honesty, if one is planning any type of non-recreational decompression dive after surface O2, this thread should be the last thing that has anything to do with how they are planning it.

A simple question regarding 'cleaning up' on the surface from recreational dives was asked and answered... a few additional points were made about how difficult it would be for a recreational diver to start to even get close to CNS limits via O2 on the surface... NONE of that has anything do with technical dive planning nor was it intended (I am sure) to be used for such.

I only mean to raise it as an issue if one is planning a repetitive staged deco dive after SI O2. That is very unlikely if you're doing it to get on a plane sooner, but quite possible if you're doing it as a form of washing out like Wookie mentioned.

 

[Doppler]

In all honesty, if one is planning any type of non-recreational decompression dive after surface O2, this thread should be the last thing that has anything to do with how they are planning it.

A simple question regarding 'cleaning up' on the surface from recreational dives was asked and answered... a few additional points were made about how difficult it would be for a recreational diver to start to even get close to CNS limits via O2 on the surface... NONE of that has anything do with technical dive planning nor was it intended (I am sure) to be used for such.

What she said!

 

[Steve_C]

So say on Dive 1 I pretty much used up my NDL on my Sunnto but not my Aeris. I am diving 30%. I have a one hour SI before a second dive to 80 ft or so. I have 1100 psi left in the tank from dive 1. This is a not unusual situation for me. This thread seems to suggest that there might be a small nitrogen benefit from breathing the first tank down to 500 psi during the SI. Not any benefit that shows on the computers/tables but a small (tiny?) benefit on actual nitrogen load?

 

[kwinter]

A simple question regarding 'cleaning up' on the surface from recreational dives was asked and answered... a few additional points were made about how difficult it would be for a recreational diver to start to even get close to CNS limits via O2 on the surface... NONE of that has anything do with technical dive planning nor was it intended (I am sure) to be used for such.

Very true. But some of the answers included comments about divers breathing oxygen at 20 feet after deco dives. And some people think that if some is good, then more is better. Everyone should recognize that breathing pure oxygen on the surface or in the boat after a dive is a completely different animal than breathing it while still submerged, which opens up a whole different series of risks.

 

[Doppler]

So say on Dive 1 I pretty much used up my NDL on my Sunnto but not my Aeris. I am diving 30%. I have a one hour SI before a second dive to 80 ft or so. I have 1100 psi left in the tank from dive 1. This is a not unusual situation for me. This thread seems to suggest that there might be a small nitrogen benefit from breathing the first tank down to 500 psi during the SI. Not any benefit that shows on the computers/tables but a small (tiny?) benefit on actual nitrogen load?

Essentially, Steve, that's about it but remember, it's all a crap shoot and as silly as that strategy may sound, anything that may give us an edge -- even a small percentage edge -- is worth a try.

The added benefit of breathing something with less N2 than air during an SI is "probably" directly related to the difference in the gas you opt to breathe and air, and the resulting washout of nitrogen from breathing EAN30 would be marginal and PROBABLY not worth the inconvenience. HOWEVER, let's say that you are sub-clinically bent after dive one. Might nitrox therapy help weigh the odds in your favor for dive #2. Maybe.

In this instance, a better strategy would be to manage ascent rates (10 metres a minute until the off-gassing ceiling, then 3 metres a minute to a safety stop and then real slow to the surface) and be aware of what your body is telling you after each dive.

 

[Duke Dive Medicine]

Steve, can you clarify what you meant by "sub-clinically bent"?

 

[Wookie]

Steve, can you clarify what you meant by "sub-clinically bent"?

I don't know about Steve's definition, but to me, as I described above, when I am on a hard working dive (dragging hydraulic hoses against the current at 80 feet) I may return from the dive with no signs or symptoms except for extreme fatigue. The question is, is the extreme fatigue from a 50 year old guy working like a 20 year old, or am I bent without any other signs or symptoms. Surface oxygen makes me feel much better. On some of these dives, I actually develop a reddened area on my right forearm, which I take as a sign of DCS... Surface O2 helps there, too.

 

[Akimbo]

Beyond cost and logistics, I see no downside of a competent nitrox-educated diver using oxygen to decrease nitrogen loading for added safety-margin against DCS. We always assume we are not bent after every symptom-free surface interval. Making an O2 reped shortly after surfacing is not a treatment, it is simply a reped. This is NOT the same as treating an omitted decompression where the probability of a hit is higher than normal.

Breathing oxygen instead of bottom mix during stops, during the surface interval, or at 15-20' on a reped all reduce Nitrogen loading. Any reduction of Nitrogen loading below what your table or computer is basing decompression on adds safety margin. This is functionally equal to adding 10' to the max depth — which was common practice when diving tables in the “old days” to compensate for higher workloads, colder conditions, or just to add safety margin.

A second advantage of adding time to stops on O2 or making an O2 reped is any undetected bubble that is forming is (re)compressed while nitrogen loading is reducing, thus less likely to create symptoms or damage.

My preference is to decompress on O2 and overstay stops at 20' by several minutes or more. Since I try to avoid dives that require stops at 20' without a chamber nearby I interrupt ascent at 20' and breathe O2 at least half the time of the estimated 10' stop. Of course I continue on O2 at the 10' stop and might overstay that time as well. All the computers I have used deal with overstaying the 20' stop or the interrupting ascent toward the 10' stop without excessive whining.

I don’t pack O2 during recreational dives. I will switch to O2 if some is hanging at the stop or make a leisurely O2 reped.

Maybe I am just lucky or have fortunate hyperbaric genetics but I have never been aware of any DCS symptoms even when other divers have been hit on the identical profile. All of my chamber rides were because I was being paid or for fun (OK, sometimes both). I hope to keep it that way.

 

[Doppler]

Steve, can you clarify what you meant by "sub-clinically bent"?

I don't know about Steve's definition, but to me, as I described above, when I am on a hard working dive (dragging hydraulic hoses against the current at 80 feet) I may return from the dive with no signs or symptoms except for extreme fatigue. The question is, is the extreme fatigue from a 50 year old guy working like a 20 year old, or am I bent without any other signs or symptoms. Surface oxygen makes me feel much better. On some of these dives, I actually develop a reddened area on my right forearm, which I take as a sign of DCS... Surface O2 helps there, too.

Essentially what Frank describes... "diver's flu" complement complex activated most likely, feeling sub-par, fatigue, perhaps some mild tingling, but no specific pain.