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Safety stop with 100% O2

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Herbert

New Member
Sep 9, 2003
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I am taking 100% O2 after all my deep dives to prevent the risk of DCS. My (hyper baric) doctor does not want me to take it under water, mainly because he thinks it is dangerous when not done properly and the risk of others doing it wrong when following my example. O2 is dangerous under pressure:naughty !!!

Nevertheless, I have been taking O2 at 6m after most of my dives, before reaching the surface. Now that I want to make deeper dives, I think it would be better to stop even earlier (deeper) – at around 25m and take Nitrox (~50%) and then switch at 6m to 100% O2.

Here comes my question to those knowing what happens in a freediver’s body:

Could I start taking 100% O2 at ~25m and slowly go to 6m? I know by scuba rules, this is insane and probably deadly, but I assume that having a lack of O2 and the short time until reaching 6m, reduces the toxicity of the O2 pressure. What do you think?
:duh
 

ash

New Member
Nov 5, 2002
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Herbert

I am no expert but I’ll chip in with my thoughts.

The broad concept of what you're describing would be fairly standard practice for a technical diver who was using 2 decompression gasses (50% and 100% O2) to decompress from a dive that had a decompression obligation.

However the generally accepted maximum partial pressure of O2 in water is 1.6ATA and then only for a limited time in a state of very little physical exertion. So 100% O2 at 6m is at the upper limit but 50% O2 is beyond the 1.6 limit at 25m (PO2 of 1.75). Usually the 50% O2 decompression gas is deployed at 21m where the PO2 is 1.55.

You’re absolutely correct that breathing 100% O2 at 25m would be considered insane from a scuba and a hyperbaric medicine standpoint. That’s a PO2 of 3.5, which is well beyond the maximum generally used in dry chambers for hyperbaric O2 treatments.

Oxygen toxicity is one of the most difficult things to predict in technical diving, a diver may be fine over any number of dives where he breathes gasses at a PO2 of 1.6 and he may display symptoms of toxicity on his next dive. At 3.5, the results would be anyone’s guess. The worst-case scenario is that the diver goes into convulsions, which will often lead to drowning.

I would personally never breathe a gas that had a PO2 of more than 1.6 unless it was a life or death situation. Better by far to be conservative and keep your PO2s down especially in the virtually unknown and untried circumstances of a freediver returning from a demanding deep dive. The short time at the high PO2 may make a difference but it would be very difficult to predict what would happen.

I could well be missing something from a freediving point of view but I hope this helps.

Ash
 

efattah

Well-Known Member
Mar 2, 2001
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It does seem that since the freediver has a 'lack' of O2, that breathing very high O2 pressures might be 'okay' for a short time. However, it may be the opposite.

I have read that when you breathe very high oxygen pressures, the O2 forms superoxide radicals (O2-). These superoxide radicals must be neutralized by your body's natural supply of superoxide dismutase (SOD), whose main purpose is to neutralize superoxide radicals.

During the freedive, when the freediver passes around 67-80m, he goes into the O2 toxicity zone, where production of superoxide increases, and as a result, he burns up much of his natural supply of SOD in order to neutralize these superoxide ions, WHILE STILL AT DEPTH. As he ascends, he may have just narrowly avoided a HYPERoxic blackout....

Then, as he ascends further, the decreasing pressure makes him start to run out of oxygen, but this only starts around 35-30m. If he started breathing 100% O2 at any depth (25m, 6m, or whatever), he must realize that he has already exhausted some of his supply of SOD because he was already exposed to incredibly high O2 pressures at depth. For example, on the sled at 120m, he experiences 13atm*0.2 = 2.6atm O2, minus a tiny bit caused by O2 consumption.

So, given that O2 toxicity is a function of how long you are exposed to high O2, then the ascending freediver has already been exposed to crazy high O2 for some time at depth, and now he starts breathing pure O2 again -- he has very little SOD left, and he could experience O2 toxicity in a pretty short time.

That's not all. Free radicals (especially O2-) are generated primarily during the REOXYGENATION phase. So, when a freediving does an 8'00" static, free radicals are mainly formed during his first few breaths, when he REOXYGENATES. The faster he reoxygenates, the more free radicals are formed. The worst possible case is to go from very hypoxic (i.e. end of static, or end of dive) and then inhale 100% O2 (or even more at pressure). This would result in even more free radicals forming. So, if the freediver breaths 100% at 6m on the ascent, and he was already hypoxic, then he creates even more free radicals than ever.

A better method might be to stop at 25m and then start breathing regular compressed air. Then, make several deco stops on the ascent. Either way, it would be beneficial to take huge amounts of antioxidants. I've heard you can even get SOD in sublingual form (you can't swallow it because it is destroyed in digestion). Apparently there are also some herbs which increase the body's production of SOD. I have also read some papers which did experiments with various drugs which delay oxygen toxicity dramatically (up to 2 or 3 times longer than usual). I have also read about some studies which said that not eating for many hours can increase resistance to O2 toxicity.

As this problem of DCS gets more and more complicated, the method of diving with less than a full breath of air becomes more and more attractive....

Just my opinion.


Eric Fattah
BC, Canada
 

Herbert

New Member
Sep 9, 2003
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Thanks Ash,

but the scuba theory is not what I am interested in – I know most of that. What I am more interested in, is the affect of O2 while freediving.
 

Herbert

New Member
Sep 9, 2003
57
38
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Thanks Eric

Seems like there is no easy answer to my question.
You are bringing up even more questions.

Since I have been using O2 for a while in training and records and have not felt anything, I a wondering what the affect of those freed radicals are on the body?

Most of my training will be totally empty or halve filed lungs, but for maximum depth I have no choice (because of equalization), so I need to find the best way of avoiding DCS (with full lungs at maximum dives).

You write that the beginning of reoxinatation is the most critical phase, so what do you think of taking air at 25m and then 100% O2 at 6m. The only down side I see is that the risk of DCS grows with taking air at 25m. It would also be an idea of only taking one breath of air or O2 at 25m and holding breath until 6m.
 

efattah

Well-Known Member
Mar 2, 2001
3,294
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Herbert,

I would definitely take my 'first' breaths of air from compressed air, whether at 25m, 10m, or 6m. You could then switch to O2, but even that is not entirely necessary; you could still decompress on compressed air, it would just take longer. You might even consider using a scuba diving computer, in scuba mode, as long as it is not one of those computers which gets 'angry' when you go up to fast. When you start deco, the computer might have some idea how long you must stay there. Or you could use scuba software to simulate the dive in advance to try to calculate how long to deco.

Diving with half-empty lungs of course brings equalizing problems. You can use various methods of bringing clean saline down with you; either taking a mouthfull of saline before you go down, or filling a big mask with saline and then sucking the saline through your nose, etc., all these methods are quite difficult. With 'sterile' (antibacterial) saline, even if you 'screw up' and get saline into your eustachian tubes, there is little chance of infection. Of course, I try to avoid getting water in the eustachian tubes. Of course, in an AIDA competition, you are not allowed to flood the mask, so the only choice is taking the saline in the mouth, which is probably the hardest of all techniques.


Eric Fattah
BC, Canada
 

Herbert

New Member
Sep 9, 2003
57
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Are you just reducing the volume in your mouth with that saline solution or are you actually getting it in you sinus?

I have tried flooding my sinus before diving with a saline solution and with sea water in the warmups, but in both cases I ended up getting lots of water in my eustachian tube.
 

Timo-Denmark

New Member
Oct 22, 2002
10
2
0
Hi Herbert - Actualy if you where calm and relaxed there will not be that big a problem, to tolerate the sort time of a high pO2 - during treatment in hyberbaric chambers the clients may be exposed to a pO2 of up to 3 bars and extended period - but if the clients move to much, doesent relax there will be a onsett of oxygencramps caused by the high pO2 - så thats not the way of dealing with the problem.. The high pO2 will most likely hit you very hard resulting in severe cramps , and more... :naughty

The way is to breathe heliox - it still washes the N2 out rapidly and mixed corectly its safe to use.. try a 40% mix... That will be usefull to about 30 meters... :D ( rember to consider the reverse flow of N2 if you change back to air, ect ect )

:wave Hopes this helps....


Timo Jattu.
 
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efattah

Well-Known Member
Mar 2, 2001
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Some comments:

1. Herbert, the saline-in-the-mouth technique I refer to involves getting the water from your mouth into your sinuses. In theory you could do it upright on the sled; I have only done it inverted during FRC CW dives. It is about 100 times more difficult than doing a regular 'mouthfill' equalization! During the first 20 times you need a buddy to come down all the way and make sure you don't choke (best to practice with mostly empty lungs) -- you can also practice on dry land by sucking water into the mouth and then bending forward. I used Seb Murat's method of tilting the head closer to horizontal during the actual equalization to avoid getting water in the tubes. The whole sequence of taking the last breath, drinking saline from a glass, then equalizing with air for the first 20m, is very, very complicated. I haven't yet done it in a relaxed way yet.

2. Timo & Herbert: Are you sure using Heliox is wise? Kirk always told me that helium is such a 'fast gas' that you absorb it very rapidly, and I'm quite sure you can get deco sickness from helium bubbles in the blood, just like N2....


Eric Fattah
BC, Canada
 

Timo-Denmark

New Member
Oct 22, 2002
10
2
0
Yes - Helium is very fast, both in and out - so it means that you must follow a slow (normal) accent rate, to awoid decompresion sickness and if in a hurry changing to 100% oxygene at aprox 6 meters. But you can actualy calculate the safe dept on Helium, the tisue has a maximum overload before it develops bubbles, if you plan the dive in according to this, there is no problems... or simply using a safe mix, wich is A% oxygene and B% oxygene, where the B% does not load the tisue with He excess the maximum overload point for the tisue - In short the tisue must not develop bubbles if withdrawn from the dept to the surface very rapidly. I have not searched out the maximum load of He in human tisue, and im aware that making such a safe gass might show to contain little He.. :)

And yes He disolved in the tisue and blood can give decompression sickness like N2 - But that goes for all gasses, it the tisue load is to big there will be a formation of bubbles nomater what relatively inactive gass you are useing ( Active gasses will do a lot more, and might kill you! ).. Even O2 might give decompression sickness, if the partialpressure is high enough and the speed to the surface is great enough - Normaly O2 is not consideret as a factor to DS, because the oxygene is metabolized in the human cells, and you proberly get hit quite hard with O2 toxisity, while trying to get DS diving on O2.... Earlyer commercial divers used a Argon mix as deco gas, but that stopped after it leaked that the commercial divers where heavyly stoned while useing this gass. ( and some acidents i gues )
 
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Herbert

New Member
Sep 9, 2003
57
38
0
Eric,

do you do a regular ferencel (pinching your nose) with the saline solution and isn't it more effective to do it under pressure?

Timo,

thanks, but I am a little lost there. Why is an He o2 mix better thena N2 O2 mix. How does this play together - having high N2 and adding He... I am lost there.
 

Timo-Denmark

New Member
Oct 22, 2002
10
2
0
Hi Herbert

Well here goes.. All diffusion, does more or less follow the fick law of diffusion.. the law describes that the flux trough a medium i determed by the a diffusion constant D, the gradient between the two compartments [pN2A-pN2B] , and the distance between the two compartsments L.... flux = D*A*[pN2A-pN2B]/L

So breating O2/N2 mix will decrease the gradient between the two compartments.. Using a mix without N2 will give the maximum gradient and thus fastest removal of N2 from the tisue. Using a He/O2 mix will of cause mean that in the beginning the He will difuse into the cells and if there already are N2 boubles make them larger. This effect is awoided by using a quite high consentration of O2, wich ensures that the He uptake is less than the initial N2 decrease - so you get a net faster decompression I think its about 40% Heliox... But i think that Divers Alert Network did some research on this topic, they surely know the right mixture...

Let me know if this makes sense !

Best regards

Timo.
 

efattah

Well-Known Member
Mar 2, 2001
3,294
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Herbert,

Here is the 'theory' behind my version of the saline technique:

- Using the standard 'mouthfill', eventually the mouthfill of air is used up; some goes into the eustachian tubes, but most of it is used in the 'dead' spaces of the sinuses and back of throat area.

- By doing a 'mouthfill' in which most of the fill is actually water, then, there is both air and water in the 'fill'; the air will go into the tubes, and at the maximum depth, the 'dead' spaces will be filled with water

This means that in my version of the saline technique (similar to Seb Murat's), there is a limit to the depth you can reach, before water enters the tubes. Using Pipin's technique, there is no limit to the depth, because the tubes become filled with water.

This is the procedure I use:
- I float upright holding a 'glass' of saline which contains a precise amount (I think it is about 150ml -- I can't remember)
- I take my last breath, the open my mouth wide, tilt my head back, and pour the saline into my mouth
- I turn inverted and begin the dive
- For the first 20m, I have to tilt my head way back (as if looking toward the bottom like a beginner diver) ; this keeps the water in my mouth, and I equalize with standard frenzel, with air
- There are two reasons why I must do that in the first 20m:
1. My mouth is too full of water & air to properly allow the water to move into the sinuses
2. The pressure change in the first 20m is too fast; and moving the water from the mouth to sinuses is time consuming
- Once I get to 20m, I slow a bit, then I look towards the line and actually touch my chin to my chest and bend forward a bit
- I concentrate hard on opening my soft palate
- The water starts to 'leak' past the soft palate into the ears; this causes a choking/drowning sensation which takes many, many times to control & resist
- Only some of the water will leak into the sinuses. The rest stays in the mouth
- During the 'transfer' process, you cannot equalize (and shouldn't)
- Soon the pressure on my ears means I must equalize. I stop the transfer, tilt my head back (like a beginner looking towards the bottom), and then do a frenzel equalization -- keeping the head tilted that way prevents the water from going into the ears
- Then, once the equalization is done I tilt my head forward and touch my chin to my chest, open my soft palate and allow more water into the sinuses
- I keep repeating
- This technique would be WAY easier just starting with a high volume mask filled with saline (and wearing a contact lens in one eye); that way you would keep your head tilted back the whole time and there would be no choking sensation as water moves from the mouth to the sinuses -- again the stupid AIDA rules makes us nearly drown ourself to prevent out eardrums from breaking


Eric Fattah
BC, Canada
 

Jon

Dairyland diver
Supporter
Apr 7, 2001
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Just my take on it.

02 used duiring deco can cause middle ear decompression sickness. This is because it gets metabloized by the body, where inert gas just stays in there once you've cleared your ears. This was a concern brought to my attention many years ago by a local diving physcian when he learned I was doing 02 deco at 20' after deep air dives. HE said that navy seals, using 02 rebreathers have had this problem in the past, but I never did.

In dry chambers people will breath pure 02 as deep as 60', but things are much different when wet. Which is why in water depth is limited to 20' with air breaks every 12 minutes or so- to toggle the CNS clock so we don't overload it.

I have done lots of dives while using 50% deco gas at 70' and 02 at 20'. We usually hang at a gas switching stop for at least 5 minutes before we head up to the next stop because it is thought to take that long get a complete circulation of blood, and gas through the body- I hope I said that right, Ash might be able to say it better.

Water, especially cold water, can bring on toxicity symptoms much quicker than in a dry chamber. You can try to follow the VENTID symptom list, but toxicity hits can happen without warning. Drugs, like psuedophed, can also trigger toxicity.

Helium is added to deco gases on deeper dives because it is a fast in/ fast out gas. On long dives, say 50 minutes @ 130', we can actually shave a few minutes of deco off by adding some helium to our nitrox mixes. This means that the tirox, or helitrox as some people call it, will allow you to off-gas faster than a normal nitrox mix. We dive a 28/30 mix on a local wreck in 135' of water and I am able to get out of the water about 3 minutes quicker than those divers breathing 28%- plus, I have no narcosis.

I am not sure about going to a straight heliox mix, with no nitrogen at all, but adding 15% -20% helium to your nitrox deco gas is done on a regular basis for very deep and/or long dives.

02 would seem, to me, to be the simplest way to go about it. It's cheap and you can get it fairly easily, in the states at least. Spending all that time mixing up custom deco mixes get time consuming and costly. To mix up triox deco gases I would want to use a helium anayzer ($800) and an 02 anlayzer($250), plus a gas whip with a digital guage($300 if you do it on the cheap) and then the 02 clean tanks to mix the gas in- which aren't any more expensive but take time to clean so you can mix safely. THis drives up the costs for 'freediving'.

Compare this to 02, which you can just use a hooka hose off of your support boat, and it makes life much easier. I wouldn't try to use 02 below 20', but then again I can't freedive to 300'.

I've read that Tanya breaths 02 after deep dives. Have you asked her about it yet? she seems to have some of the best support crew around?


Just my $0.01- since i don't know if it's even worth a full $0.02;)

Jon
 

tom yerian

New Member
Sep 26, 2004
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Herbert said:
I am taking 100% O2 after all my deep dives to prevent the risk of DCS. My (hyper baric) doctor does not want me to take it under water, mainly because he thinks it is dangerous when not done properly and the risk of others doing it wrong when following my example. O2 is dangerous under pressure:naughty !!!

Nevertheless, I have been taking O2 at 6m after most of my dives, before reaching the surface. Now that I want to make deeper dives, I think it would be better to stop even earlier (deeper) – at around 25m and take Nitrox (~50%) and then switch at 6m to 100% O2.

Here comes my question to those knowing what happens in a freediver’s body:

Could I start taking 100% O2 at ~25m and slowly go to 6m? I know by scuba rules, this is insane and probably deadly, but I assume that having a lack of O2 and the short time until reaching 6m, reduces the toxicity of the O2 pressure. What do you think?
:duh
Your dancing with the devil on that one. To say, " if you take even one breath of 100% o2 at a depth greater than 20fsw, you will take an oxy. hit , is not exactly true. US NAVY used to do oxygen tolerance tests to sixty fsw for thirty min. in the early days of dive testing.That was dry tests in a chamber though. I have Taken several hits of 100% o2 as deep as 50 feet, switched to air, took some hits, switched,etc. I was experimenting, it wasn't smart to do, especially since I had no back up. So, don't do it. Everybody's different, 02 reacts different on divers, etc. Be safe; don't do it!!... Capt Tom
 

island_sands

Erection Supervisor ;)
Supporter
Jan 19, 2001
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tom yerian said:
Your dancing with the devil on that one. To say, " if you take even one breath of 100% o2 at a depth greater than 20fsw, you will take an oxy. hit , is not exactly true. US NAVY used to do oxygen tolerance tests to sixty fsw for thirty min. in the early days of dive testing.That was dry tests in a chamber though. I have Taken several hits of 100% o2 as deep as 50 feet, switched to air, took some hits, switched,etc. I was experimenting, it wasn't smart to do, especially since I had no back up. So, don't do it. Everybody's different, 02 reacts different on divers, etc. Be safe; don't do it!!... Capt Tom


I once took a hit of 80% at 30m.. and didn't realise the full effect until i reached 18m (we were making an ascent). Lucky my dive buddy/instructor was fast thinking... I convulsed on the surface after he had assisted my ascent.
not a pleasant experience.
 

johnnybuoy

cork spearo
Mar 14, 2008
1,043
135
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How did u manage to breath 80% at that depth???? Jesus. That's a ppo2 of over 3!! How did you manage that??
 

EddieP

Member
Sep 14, 2011
20
1
13
It would also be an idea of only taking one breath of air or O2 at 25m and holding breath until 6m.

25m to 6m is 3.5bar to 1.6 bar therefore the pressure is over 2x difference. Anyone else expect hyperbaric trauma?
 

ReefTroll

Expert Space Drummer
Apr 9, 2008
1,712
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Bit left field here but I find threads like this amazing. They show how much there is to learn about our own bodies. So many years of research by some incrdibly brilliant people, yet so much to discover.
 
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