DCS cure using pure02 or Nitrox mix

[sipadiver]

RE: SAFETY STOP USING 02 or Nitrox.


Hi. I'm doing my Divemaster course and learning all about the wonderful world of gases etc..

Just then a thought struck me.

Hypothetical question - What if a diver had spent too long under the surface - lets say for example he spent 40 minutes at 40M. He was using regular air. (The group is out at sea in a small dive boat - they have an emergency 02 bottle.)

Let's say he got lost or stuck somewhere under the sea. His safety stop would outlast his air supply. Air tanks are dropped down to help him decompress longer.

Would it help prevent DCS if a tank of pure02 or Nitrox was lowered to 5M so that he can decompress faster or at the very least be more beneficial than breathing ordinary air?

I know that breathing pure02 at 2 atmosphere is deadly. But at 5m what would the effect be for 10minutes?

If that is too hazardous - would a Nitrox mix of 30%O2 be more helpful than just normal air?

 

[Storker]

I'm not a doctor, but since I'm rather risk adverse, I'd be leery about providing pure O2 underwater for a run-of-the mill rec diver without deco training. Lose buoyancy control, drop to 10m and presto, they're at 2.0 ATA pPO2...

Nitrox would accelerate the off-gassing compared to air due to the lower pPN2. However, to be on the safe side I'd try to stay for the time needed to complete deco on air if that was possible. Otherwise, this would be an appropriate time to break out some deco software or tables...

 

[sipadiver]

Yes, of course. But lets say the diver is competent. (He just got stuck somewhere… say a giant octopus dragged him down to 40M for awhile)

I'm just thinking of what's available on the dive boat that could possibly help him as he was doing his safety stop. Usually a boat would carry an 02 bottle. Could that be used for his safety stop?

Would it be OK to breath pure 02 at 5 Meters ?

This is just an academic question…

 

[Redshift]

It could help decompression, but how and why you can learn in any decompression course, not DM.

 

[Johanan]

Generally, nitrox will speed up offgasing and shorten the required deco time. One can safely breathe pure oxygen from 6m and up. Let's say, 80% might be more helpful as you can start breathing it deeper and the overall result could be better. It is advisable to indicate the oxygen content and maximum depth on the cylinder.

10 minutes is a guess. If gass is available, I would follow the computer indications, and if I would surmise that I skipped necessary deco stops, I would grab the provided cylinder, return to some 15 metres or as deep as the mix allows, stop for a minute, than ascend to 12m, stop for two minutes, 9m, 3min and spend plenty of time at 6m. As long as the gas lasts, may be. It is one of the skipped deco procedures. But it's theoretical and would work only if appropriate Nitrox cylinders are available.

Don't take my word, but rather read the Deco Procedures manual and play with some dive planning software. Even better, take the Advanced Nitrox and Deco Procedures course.

 

[Storker]

Would it be OK to breath pure 02 at 5 Meters ?

You haven't taken a nitrox course, I see.

5 meters on pure O2 is 1.5 ATA pPO2. You plan for a max pPO2 of 1.4, but accept 1.6 in a pinch. The body can tolerate somewhat higher pPO2 at rest, so personally I wouldn't have a problem breathing from an O2 bottle if I were hanging at 5m. However, I'd make pretty darned sure I had a line to hang on or a hard bottom just below me. And a buddy.

This is just an academic question…

If so, I'd go for the KISS principle. O2 on the surface to use if you suspect a DCS hit, or if there's omitted deco. Breathing gas that the diver is trained for to be lowered to their emergency deco stop. Deco times calculated for air as the deco gas, any benefit from breathing nitrox during deco is considered a bonus.

 

[victorzamora]

Just to let you know, 40m for 40 minutes means an hour of deco stops on air and O2 with my "usual" conservatism. Even with bare-minimum conservatism, you'd have nearly 30 minutes of total deco obligation and over 20 minutes on O2. I'd put the diver on O2 on the boat, and then the highest percentage nitrox mix, and I'd call ahead for O2 to be prepared. If they go symptomatic, I'd call DAN.

But to answer your question, yes. In that situation, the less nitrogen they're breathing, the better. Period. Getting a diver in the water with oxygen can be dangerous, but with calm seas and a good diver and a good tender it might be okay. O2 on the boat followed by highest percentage nitrox available until he's breathing air. No point in breathing compressed air, so unless you have nitrox just let him breathe the atmospheric air.

 

[DevonDiver]

What you're asking is whether >21% O2 is beneficial to off-gassing / decompression.

The short answer is YES.

This practice is what technical divers learn as 'accelerated decompression'. The principle is just as applicable to 'emergency decompression' as it is to planned decompression.

I'm not suggesting that divers utilize mixtures that they aren't trained to use. There are dangers, especially with O2 mixes considerably richer than recreational nitrox qualifies for.

Richer O2 mixes increase the gas gradient between tissues and ambient pressure. The higher gradient leads to faster off-gassing.

Qualified decompression divers can plan shorter decompression, based on higher O2 decompression gasses.

If richer O2 gasses were used for emergency decompression, then it should be done for conservatism... not calculated to reduce deco time... but rather to increase the comfort margin against DCS.

I know many dive operations that use 32, 36 or even 40% as standard, in emergency drop tanks (standard for deep dives).

One issue to consider, however, is gas analysis. Any diver breathing that gas SHOULD have analyzed it PERSONALLY. No exceptions to that rule right?

Thus... Nitrox drop tanks are an issue... and the operator needs think of acceptable protocols if they're going to implement it...

Using 100% is great... but you need to ensure there's no way the mix could be breathed below 6m (at 1.6 ppO2).

For many recreational divers... I'd have concerns over the necessary discipline, awareness, focus or buoyancy control to guarantee that. Thus... no pure O2 for recreational divers.

 

[doctormike]

RE: SAFETY STOP USING 02 or Nitrox.


Hi. I'm doing my Divemaster course and learning all about the wonderful world of gases etc..

Just then a thought struck me.

Hypothetical question - What if a diver had spent too long under the surface - lets say for example he spent 40 minutes at 40M. He was using regular air. (The group is out at sea in a small dive boat - they have an emergency 02 bottle.)

Much of what you are asking is the course material for the deco procedures course, and probably best learned in that context, rather than having you try to piece it together from a few internet forum posts... however, it's good that you are interested, and maybe I can explain things a bit so that you will have some useful insight into this topic. Sorry I don't speak metric that well..


1) I wouldn't use the term "safety stop". That implies some extra time for a diver with no deco obligation. What you are describing is "unplanned deco". "Omitted deco" would be what you would happen if you surfaced without doing the required decompression.


2) As far as maximum safe depth, this is something that would be covered in a nitrox class (you can do DM without nitrox? Didn't realize that). For deco gas, we generally use a ppO2 of 1.6 ATA, so for 100% O2 that's about 20 feet.


3) Yes, mixes with lower nitrogen content (enriched air nitrox, EAN) do result in faster decompression, for a given profile. But as mentioned elsewhere, an untrained diver breathing a high O2 mix now involves the risk of oxygen toxicity if he or she inadvertently goes below the maximum operating depth (ppO2 1.6) of the gas involved.


4) The question of whether you can safely complete the required deco obligation at at standard 15 foot "safety stop" would be determined by whether or not your ceiling (the shallowest depth that you can safely ascend to before stopping to decompress) is above 15 feet. The ceiling changes during the dive based on accumulated nitrogen.


5) I put the particular case that you described (40 minutes, 40 meters, breathing air) into multi deco, just to give you an idea of the deco obligation involved. Using some standard assumptions (GF 30/75), you would need to stop for 1 minute at 60 feet, 4 minutes at 50 feet, 6 minutes at 40 feet, 10 minutes at 30 feet, 7 minutes at 20 feet and SIXTY TWO minutes at your "safety stop" depth of 15 feet! A total of 92 minutes of deco. At my SAC rate, it would require 254 CUF of gas, more than I have in my double 119s.


6) If you had the ability to switch to 100% O2 at 20 feet, you would still have to make those deeper stops, but you would only need to spend 3 minutes at 20 feet and 17 minutes at 15 feet.


7) If you want to go by the absolute Buhlmann maximum "ceiling", basically trading operational advantage for DCS risk (i.e. getting you out of the water as fast as possible), that would be a GF of 100/100, so you would be riding the "M value line" and staying just below the ceiling. A bad idea with a high likelihood of DCS, but I think that might be what the OP is asking. That profile would be 2 minutes at 30 feet, 4 minutes at 20 feet, and 35 minutes at 15 feet. About 200 CUF for that dive, doable with double 119s (leaving aside the increased SAC rate from this emergency).


8) So what would probably be actually done in the OP's hypothetical situation would be for the diver to stay on the line at 15 feet, drain his back gas tank and maybe another air tank if it could be lowered to him, go on the 100% O2 once on the boat and head for a chamber.

 

[Storker]

no pure O2 for recreational divers.

You mean underwater, of course.

I'm not trying to pick nits here, I just want this to be totally clear, since it seems the OP hasn't been taught this. It is of course quite OK - and a good thing - to provide O2 on the boat/shore if one suspects a DCS hit, or if the diver owes deco on surfacing.