Nitrogen bubbling and Oxygen

[iainwilliams]

Hello

I wish to discuss 2 scenarios to maximise nitrogen elimination..

A shallow dive (less than 10 m) produces more absorbed nitrogen in our slow tissues whilst a deep dive absorbs more nitrogen in our faster tissues. Micro-bubbling, which is “mainly” dependent on exposure time and ascent rate, can occur in both circumstances, although it is best that it does not occur at all!

QUESTION: Which method will remove more nitrogen from your system.

1. Using EAN 40 and switching at a deeper depth – probably before micro bubbling may occur. This would give great oxygen tissue saturation at a deeper depth, but still allow nitrogen on gassing; or

2. Using 100% oxygen at 5 m (1.5 PO2) which would provide 100% oxygen saturation, but probably after micro bubbling has occurred?

Thank you…………..Iain

 

[Saturation]

iainwilliams once bubbled...
Hello

I wish to discuss 2 scenarios to maximise nitrogen elimination..

A shallow dive (less than 10 m) produces more absorbed nitrogen in our slow tissues whilst a deep dive absorbs more nitrogen in our faster tissues. Micro-bubbling, which is “mainly” dependent on exposure time and ascent rate, can occur in both circumstances, although it is best that it does not occur at all!

QUESTION: Which method will remove more nitrogen from your system.

1. Using EAN 40 and switching at a deeper depth – probably before micro bubbling may occur. This would give great oxygen tissue saturation at a deeper depth, but still allow nitrogen on gassing; or

2. Using 100% oxygen at 5 m (1.5 PO2) which would provide 100% oxygen saturation, but probably after micro bubbling has occurred?

Thank you…………..Iain

Hi Iain:

A good way to maximize N2 elimination is to minimize uptake at depth and maximize elimination before and at surfacing.

During dives, use the largest nitrox percentage safely allowable. Triox is even better as Helium mechanics are more predictable during the off gassing phase. If this means switching gases at depth, this must be weighed over its logistic complexity in non-decompression diving.

At the safety stop, use 02.

The best way is not to breath N2 if at all possible, which means Heliox within recreational depths.

Only by diving very deep is it theoretically possible to crush microbubbles enough to reduce its concern during decompression. This would be in the order of dives past 160.'

Microbubbles are always a consideration in dives. Its not their existence, but their radii that is a problem. What microbubbles are, are well discussed by Dr. Deco somewhere on this eboard.

 

[iainwilliams]

Thanks saturation.

I guess accelerated decompression with 100% O2 at 5 m is better than just using a high nitrox mix with no 100% O2.

Most of my diving is on air and I switch to 100% O2 at 5 m for the safety stop. Sounds like this practice is the best one to outgas N2 and minimise DCS. If I want to be safer - then use nitrox also (taklng into account O2 toxcity of course).

Thanks again.............Iain

 

[BRW]

Diving any EANx and riding it thru deco stops without
pure O2 at 20 fsw will ALWAYS give longer deco times than
riding same EANx up to 20 fsw and then a switch to pure O2

Switching from air to something like EAN40 or EAN50
in the intermediate zone (say 60 fsw), and then to pure O2
at 20 fsw will ALWAYS result in shorter deco time than
just switching to pure O2 at 20 fsw.

If you are diving trimix, then things get more complicated.
It becomes a question of riding trimix to 20 fsw and pure O2,
versus some isobaric switch to some EANx at ppO2= 1.4, and
then onto pure O2. Such depends on depth, time, and EANx

 

[iainwilliams]

Thanks guys

 

[BRW]

Diving any EANx and riding it thru deco stops without
pure O2 at 20 fsw will ALWAYS give longer deco times than
riding same EANx up to 20 fsw and then a switch to pure O2

Switching from air to something like EAN40 or EAN50
in the intermediate zone (say 60 fsw), and then to pure O2
at 20 fsw will ALWAYS result in shorter deco time than
just switching to pure O2 at 20 fsw.

If you are diving trimix, then things get more complicated.
It becomes a question of riding trimix to 20 fsw and pure O2,
versus some isobaric switch to some EANx at ppO2= 1.4, and
then onto pure O2. Such depends on depth, time, and EANx


__________________

 

[Saturation]

iainwilliams once bubbled...
Thanks saturation.

I guess accelerated decompression with 100% O2 at 5 m is better than just using a high nitrox mix with no 100% O2.

Most of my diving is on air and I switch to 100% O2 at 5 m for the safety stop. Sounds like this practice is the best one to outgas N2 and minimise DCS. If I want to be safer - then use nitrox also (taklng into account O2 toxcity of course).

Thanks again.............Iain

Hi Iain:

Yes, you have it. But I'm now a tad confused. Dr. Wienke's reply suggests you are doing decompression stop dives, and my read on your question is that you are asking about ways to reduce exposure to N2 in no-stop dives.

If we are talking about deco dives, this is a completely different animal, so I presume its not.

A risk for DCI to recreational divers is ~1/1000 divers, other comparisons made by the US sports industry is that relative to how they gather their numbers, DCI risk in recreational SCUBA is roughly equivalent to injuries in bowling.

02 at 15' for NSL dives is not necessary but you will accelerate N2 offgassing. If you breathe 02 routinely, you trade off a very low risk of DCI in recreational dives with a risk of 02 convulsions and possibly death, an acceptable risk for those trained for this procedure and particularly if necessary as in decompression dives. If one were looking at a procedure for routinely breathing 02 after a recreational dive, it is safer and simpler to breathe it on the surface for 10 min versus 5 minutes at 15' since its strictly not required in the first place.

To breathe 02 in-water requires technical training, and with it comes a host of issues covered in an "advanced nitrox" curricula provided by any technical training agency.

No data I know defines how long to breath 02 in a NSL dive, since it isn't necessary.

Since its known a 3-5min safety stop on air substantially reduces bubbles in NSL dives, its logical to assume substituting 02 at the safety stop would wash out N2 and potentially microbubbles even better. 1 ATA 02 for 10 minutes is just a logical extension of breathing 1.6ATA 02 for 5 minutes, it doesn't mean its as effective, but in simple recreational dives, its a good trade off.

 

[Dr Deco]

Dear Readers:

Oxygen

As has been mentioned, oxygen usage by recreational divers is not really an optimal method of reducing DCS risk. It is really better to avoid nuceli formation in the first place. You do not really have sufficient oxygen in most cases to make a difference - and NDLs are safe to start with.

Dr Deco :doctor:

Please note the next class in Decompression Physiology
http://wrigley.usc.edu/hyperbaric/advdeco.htm