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Diving on 100% Oxygen

Thread Status: Hello , There was no answer in this thread for more than 60 days.
It can take a long time to get an up-to-date response or contact with relevant users.
Yup, Inspiration.

Using it at the moment with Air diluent, but soon to be going over to Heliox to get some more depth without the Narcosis. The Helium and Oxygen cylinders are in my garage already.....

And Yes, VENTID is what I can remember from my Nitrox and Trimix courses.

Dare I ask what you were using a hacksaw on?

Pete S
That is one heck of a lot of stuff to sort out while holding your breath at 60+meters!
Kirk would be a good one to ask about this because he is a mixed gas instructor and a freediver. Many of these symptoms seem to be interchangable.
PPO calcs.

Vince you are close but not quite.

Allways work in METRIC. It's easier. Presure under water rises 1 bar per 10 metres of depth. You can do the sums in your head. Or you an work in Ats or PSI and feet. Horrible.

PP = Partial pressure of a gas in bar

D = Depth in metres

% = Percentage of that gas in the gas mix as a decimal

PP = ((D+10)/10)*%

Ex 1 PPO2 of a 50% O2 mix at 21 metres

PPO2 = ( ( 21 + 10 ) / 10 ) * 0.5 = 1.55 bar This is why 50% O2 is used from 21 metres for accelerated decompression

Ex 2 PPO2 of a 100% O2 mix at 6 metres

PPO2 = ( ( 6 + 10 ) / 10 ) * 1 = 1.6 bar This is why 100% O2 is used from 6 metres for accelerated decompression.

We normally use the equation the other way round to work out our % of O2 for bottom mix.

Ex 3 Dive to 60 metres with a max PPO2 of 1.4 bar

% = PPO2 / ( ( D + 10) / 10 )

% = 1.4 / ( ( 60 + 10 ) / 10 ) = 0.2 = 20%
Hmmmm beter do this on Trimix and sling in 40 % helium to offset Narcosis. This is NOT an air dive.

Got it? Good

Equivalent narcosis depths are the next logical step so that you can work out the Helium percentage needed. But I think that is outside the limits of this tech diving course. As are the gas blending calcs.

Pete S

It's not to hard to find the ppXX of a gas, but I was referring to the PaCO2 = arterial CO2 pressure. This is very difficult to calculate, and depends on many personal variables. For example, the lung volume, the bicarbonate concentration in the blood, the hematocrit, the total blood volume, etc... very hard to calculate, you can only approximate it.


Can you use a pulse-ox meter to measure it? I have heard Terry Mass talk about such a device used in surgery that might be adaptable to freediving. I know that you hook yourself up to other machines when training; but, have you ever tried this? If it reads po2, might it not also read co2??
Measuring PaCO2, PaO2 etc.

It is easy to measure all the physiological parameters while on land, the problem is underwater. On land, the highest etCO2 I have ever managed was 8.8% (after more than 7 minutes of apnea), just short of the 9% required to enter CO2 narcosis. However, doing a pure oxygen breath-hold on land, most freedivers can get etCO2 > 9% and enter narcosis, and some can black out from CO2 narcosis, even when they have tons of O2 left (see for example the study at Duke university).

I bet that Martin Stepanek goes over 9% etCO2 (PaCO2 68.4mmHg) during his 8+ minute statics...maybe he becomes the first person ever to get CO2 narcosis from an atmospheric air breath-hold...


During high school, I was a lifeguard for Dade County.

Many of the places I guarded at had O2 tanks to administer to people in the event of a medical emergency.

The other guards and I, for the sake of freaking people out, would hyperventilate on the O2 for a few minutes, take a good, long, deep breath of pure oxygen and slowly walk into the water, making sure everyone in the swimming area of the lake could see us. The breathing was all done inside the lifeguard shack so no one could see what we were up to.

We were allowed to pass 'The Line' that seperated the safe, shallow part of the lake from the dangerous, deep part. Every kid from every summer camp dreamed of crossing that line, but they knew it meant 15 minutes of embarrasing punishment ladled out by bored lifeguards in full view of their friends when they got caught, so most didn't do it.

Anyway, we would make sure everyone saw us cross the line, then we would submerge out of sight and swim to a buoy that was about 15 feet away from the rope. This buoy had a heavy metal bar attached to the bottom of it to help prevent it from drifting, so we would latch on to that and wait. And wait. And wait and wait and wait.

Even the O2 hogs in the group could stay under for 4 minutes, with the more efficient breathers getting around 7 minutes downtime.

After we started feeling the need to breathe, we would casually swim back under the rope, as if nothing special had happened. There would be 50 or 60 kids and about 10 counselors, all staring wide-eyed in disbelief.

The hardest part was keeping a straight face.
Re: Measuring PaCO2, PaO2 etc.

Originally posted by efattah
I bet that Martin Stepanek goes over 9% etCO2 (PaCO2 68.4mmHg) during his 8+ minute statics...maybe he becomes the first person ever to get CO2 narcosis from an atmospheric air breath-hold...

Eric [/B]

When I read Eric's article about long term effects of breath-holding, there wasn't any word about CO2 narcosis. When pushing even over 8min breath holds, is that bad for body? And if it is, just that moment or are there long term effects? How low SaO2 gets? Is the point where Sa02 drops below 80% movable by breath-up?

And btw, just to be sure, can you explain all those acronyms ;) PaO2 and PaCO2 for example?
ill give it a try although efattah might be in a better position to answer..

please someone correct me if im wrong...

paXX mean the partial pressure of gas in an artery, since not all gases are absored the same this could be different then...

ppXX which means the partial pressure of a gas look at one of my earlier post for more detail on this

hopes this helps..(if im right)
Re: Measuring PaCO2, PaO2 etc.

Only deep freedivers get CO2 narcosis (i.e. 80m+), ...


Eric I know about a case where a diver was just relaxing at a depth of 15 meters. After several minutes he felt asleep. Nitrogen narcosis is unlikely. CO2 narcosis it might be the case though. Therefore is not only an issue for deep dives but also an issue for shallow dives with relatively long bottom time. CO2 build up in SCUBA diving is likely when the work of breathing is high and it is definitely something that need to be prevented by all means.

I was wondering if anyone has every taken a dive after inhaling a lungfull of 100% oxygen? Does this increase bottom time? Do you still get contractions and the urge to breath because of CO2 buildup, even thuogh you may still have plenty of oxygen in your lungs? Where would one get a small tank (pony bottle?) of 100% oxygen? Comments?

Experience says that pure O2 can indeed increase bottom time. But this has a precondition. The diver shall be adopted to very high CO2 levels and the contractions due to elevation of CO2 would be delayed enough. The actual limit of bottom time is oxygen availability and definitely 6 litres more of oxygen can significantly increase bottom time. But the breath-in signal to your body is largely CO2 in the stage where not enough adoptation has been developed yet.

Breathing from a pony tank underwater, any gas, is against all fair playing rules and also might create serious problems including lung overexpansion injury. Furthermore breathing Oxygen at high pressures may cause CNS Toxicity, convulsions and drawning.

You said in your post that you are using a helium mix as well. This information was posted as to diving on 100% pure oxygen, no mix. Meaning that you can not safely dive while breathing off of an o2 bottle as the original poster was asking.

The information is laid out in the US Navy Dive Manual Volume 2. I recommend you examine it and see that it is clearly documented there.

Here is the exact quote from part of it. It is several pages long, so I have only inserted the important pieces:

"From the air we breathe, oxygen is the only air used by the body. The other 79% is used to dilute the oxygen entering the body. Sometimes 100% oxygen is used for shallow diving operations and certain phases of mixed gas diving operations. However, breathing pure oxygen under pressure may induce the serious problems of oxygen toxicity."

Examine it for yourself. If I am wrong let me know so I can stop teaching my classes wrong information, and I can correct my instructors who taught me.
:duh :naughty

All your information is correct.

When I'm ascending from a deep dive in cold water, in addition to the vertigo, dizziness, confusion, sleepiness, loss of concentration, metallic taste, and 'buzzing feeling', my vision definitely gets screwed up, everything is a bit faded, less clear, I hesitate to say blurry--it's like all the images are there, but my mind is paying no attention to them, as if they are far away in a distant tunnel, but right there at the same time, as if in a vague dream.


Tunnel vision is one of the characteristic symptoms of CNS Oxygen toxicity. The other symptoms are: Ear tinnitus, Nausea, Muscle Tingling especially around the mouth, Irritation, Dizziness and Convulsions. Not all individuals are equally sensitive to oxygen. CO2 concentration potentiates the O2 effects in the brain as it increases the permeability of the brain-blood barrier.

ok this is just out of curiosity cause i think might make a good school project

here is what i know (or think i know)
1 ata=14.7psi=1013mmHg

how in the world do you calculate PPO2and PPC02 this is my guess but im probably wrong

depth(m)*0.1(ata)*(% of gas)

for example: dive to 50 meters on nitrox 36% (i know it should never be done)

1.8 PP02

thanks ,vince

Correct calculations! But while applying these principles on SCUBA diving where the alveolar concentrations of gases are predictable you may not apply these rules to breath-hold diving because here it is an other story.

What is important is to focus on the partial pressures of gases that the diver is exposed to and not the fractions of gases in the breathing mix. The maximum exposure to a concentration of 1,8 ATA O2 is 2 minutes. I have no information on free diving limits though. Ox Tox can hit at pressures well below that especially when the CO2 in the blood is high. One fact about free diving is that classic Dalton's and Boyle's laws fail to explain the fluctuation of arterial gases during a deep breath-hold dive. During a breath-hold dive immersion it self, the blood shift that causes changes in the ventilation - perfusion relations, the consumption of oxygen, the rate of CO2 production and the high storage capacities of CO2 in the blood and fast tissues are complicating calculations. A lot of research is needed in this field before we come to any solid conclusion.
Hi Diveoceanos,
Your response is very authoritive but you need to check the dates on the last post of a thread this one is a few years old. Just for your own info if you are wondering why no one responded about it.
Hi Diveoceanos,
Your response is very authoritive but you need to check the dates on the last post of a thread this one is a few years old. Just for your own info if you are wondering why no one responded about it.

Hi Feargus,

Thank you for mentioning. I just noticed the dates. I don't know how I came across this thread :duh