Scuba Nitrox Incident for Analysis

[Julius SCHMIDT]

But to me the actual emergency ended when he grabbed the float. Then I was able to talk with him, move him and get him to the dock.

Your soothing voice kept everything calm John C. Ratliff. I just hope the guy with the shoes full of water is okay.

There are two threads running here, oops

 

[OTF]

We're may be getting off topic, but human breath is about 4% CO2, about 100x as much as the atmosphere. The Chemical Composition of Exhaled Air From Human Lungs

So it's not that far fetched that a small room with a compressor and people in it would have excess CO2. And since it's the partial pressure that matters, if you started with 1.5% CO2, descended to 25 meters, you'd have about the same CO2 as exhaled breath. That would eventually leave you feeling very short of breath. I admit that's a crazy high starting concentration unless you have a bunch of people respiring around a compressor in a closet.

Interesting point that I haven't heard of before. Miight be plausible on a small boat or something.

To be clear though, the CO2 in this case (and in deeper CO2 hits or 'dark narc') almost certainly isn't coming from CO2-contaminated tank gas but rather building up in the diver "naturally" from physical exertion and/or improper breathing to eliminate it fast enough. Both breath holding and hyperventilation can cause CO2 retention even at the surface. Kicking hard against strong current or doing other very physical work at deep depths is a sure way to build up a lot of CO2 at high partial pressure that will mess you up.Too much CO2 in your system does cause a panicky feeling that you can't get enough air.

Not to be confused with CO which would be coming from a contaminated tank.

 

[Angelo Farina]

To be clear though, the CO2 in this case (and in deeper CO2 hits or 'dark narc') almost certainly isn't coming from CO2-contaminated tank gas but rather building up in the diver "naturally" from physical exertion and/or improper breathing to eliminate it fast enough. Both breath holding and hyperventilation can cause CO2 retention even at the surface. Kicking hard against strong current or doing other very physical work at deep depths is a sure way to build up a lot of CO2 at high partial pressure that will mess you up. Too much CO2 in your system does cause a panicky feeling that you can't get enough air.

Sorry to correct you but you are misusing the word "hyperventilation" as a cause of CO2 buildup, while technically hyperventilation is the exact opposite: venting too much, causing the CO2 level to drop and causing a number of symptoms which have nothing to do with the cases discussed here, such as vertigo.
What Causes Hyperventilation?
Unfortunately it appears that many people in US do not know the exact meaning of hyperventilation, confusing it with its opposite case, short breathing with poor ventilating, which should be named hypoventilation. From Greek:
Hyper = too much
Hypo = too little
So if a guy hyperventilates, the CO2 will DROP too much, as clearly explained in the article I linked above.
If a guy hypoventilates (short breathing) the CO2 will GROW too much.
Hyperventilation is a practice which sometimes is employed by free divers before a very deep dive, but, as said, it can cause vertigo and other nasty symptoms.
So it would be better to avoid to confuse novel divers using improper wording.
Sorry again to correct you, I do not want to appear pretentious or patronizing...

 

[John C. Ratliff]

Angelo,

What you state for “hyperventilation” is correct, but I think is not the only definition of the term. To me, and from my training, hyperventilation occurs whenever the breathing rate is very high, no matter volume of air moved into and out of the lungs. The hyperventilation which removes CO2 and is a danger to free divers is a rapid, deep breathing prior to breath-hold diving. Because the amount of CO2 in the blood is what triggers the “must breath” response, and not the oxygenation of the blood, a free diver can overcome the need for breathing and continue swimming until blackout. I know because I’ve done that in my early years.

But the type of hyperventilation I’m talking about with this video (see the earlier post on page 1) is somewhat different. It is rapid ventilation which doesn’t really exchange much air, and re-uses the air within the scuba double hose regulator to a large extent. If you’ll count the respiration’s shown in this video, you’ll see that they are very high in respirations per minute. (I counted about 6 in ten seconds, or a breathing rate of 36/minute.). Because of these facts, with little “good air” coming into the lungs, CO2 buildup is happening.

Now, one other thing I mentioned is that he entered the water with an “oxygen debt.” This is an accepted term for the body not having enough oxygen after exercising.
Oxygen Debt & Recovery - Anaerobic Exercise - TeachPE.com

It was these combinations of factors that led to the emergency situation.

SeaRat

 

[Angelo Farina]

Angelo,

What you state for “hyperventilation” is correct, but I think is not the only definition of the term. To me, and from my training, hyperventilation occurs whenever the breathing rate is very high, no matter volume of air moved into and out of the lungs. The hyperventilation which removes CO2 and is a danger to free divers is a rapid, deep breathing prior to breath-hold diving. Because the amount of CO2 in the blood is what triggers the “must breath” response, and not the oxygenation of the blood, a free diver can overcome the need for breathing and continue swimming until blackout. I know because I’ve done that in my early years.

But the type of hyperventilation I’m talking about with this video (see the earlier post on page 1) is somewhat different. It is rapid ventilation which doesn’t really exchange much air, and re-uses the air within the scuba double hose regulator to a large extent. If you’ll count the respiration’s shown in this video, you’ll see that they are very high in respirations per minute. (I counted about 6 in ten seconds, or a breathing rate of 36/minute.). Because of these facts, with little “good air” coming into the lungs, CO2 buildup is happening.

Now, one other thing I mentioned is that he entered the water with an “oxygen debt.” This is an accepted term for the body not having enough oxygen after exercising.
Oxygen Debt & Recovery - Anaerobic Exercise - TeachPE.com

It was these combinations of factors that led to the emergency situation.

SeaRat

Technically what you wrote is entirely correct. It is just a linguistic bias, perhaps: I am not a native English speaker, and here in Italy "iperventilazione" is strictly associated with a CO2 REDUCTION, never to a buildup.
The short breathing you described is called "affanno", and no one will ever confuse it with hyperventilation, as they are actually exactly two opposite cases.
Perhaps in English this distinction is not so clear, and you do not have an exact translation for the "affanno" short breathing, which causes CO2 increase. Google Translate suggests "breathlessness" as the English word for "affanno"; but I am not sure it is the proper medical term...
Coming back to the oxygen debt: I am well aware of it, but it can only occur after an ANAEROBIC exercise. This is a very fast burst, as when running the 100 meters in 10-11 seconds. Which is not exactly the type of activity described to be occurred before entering the water... So again I think that such a physical activity did cause mostly a CO2 buildup and accumulation, not a significant oxygen debt (which, indeed, had caused no symptom, even if present)
The lack of oxygen DOES NOT trigger ventilation: if after a strong muscular exercise we feel the need of breathing more, this comes, again, from the CO2 concentration in your blood, not from the lack of oxygen.
The real problem of lack of oxygen is exactly that we have no detectors for it. And this is very well documented to what happens to patients affected by the Covid-19 disease: their blood oxygenation percentage can drop to less than 80%, and they still feel "fine" with no need to breath more deeply...

 

[boulderjohn]

The lack of oxygen DOES NOT trigger ventilation: if after a strong muscular exercise we feel the need of breathing more, this comes, again, from the CO2 concentration in your blood, not from the lack of oxygen.

There is a trigger for lack of oxygen, but it is far more subtle than the CO2 response and thus usually not noticed and not necessary.

I became personally aware of this when I was recovering from surgery and on supplementary oxygen. There were many times that even with normal breathing, my oxygen levels would drop too far, and, believe me, I knew it. This was especially true as my recovery increased to the point that I was only using a little oxygen at night. If the numbers dropped too far, I would wake up with an urgent need to breathe deeply. I had a meter by my bed, and invariably it would show that my 02 levels were too low.

 

[Angelo Farina]

There is a trigger for lack of oxygen, but it is far more subtle than the CO2 response and thus usually not noticed and not necessary.

I became personally aware of this when I was recovering from surgery and on supplementary oxygen. There were many times that even with normal breathing, my oxygen levels would drop too far, and, believe me, I knew it. This was especially true as my recovery increased to the point that I was only using a little oxygen at night. If the numbers dropped too far, I would wake up with an urgent need to breathe deeply. I had a meter by my bed, and invariably it would show that my 02 levels were too low.

What happened to you is true. I also had major surgery past September, and I had the same feeling of lacking air.
When you do not ventilate enough the blood oxygenation drops.
But simultaneously CO2 increases...
It is the latter giving the "need for air" stimulus.
If the oxygen goes down, the hemoglobin cannot swap it with CO2, so the latter accumulates and gives this effect.
So it is true that when some medical condition prevents proper gas exhanges, O2 goes down. But simultaneously CO2 goes up, stimulating the need of breathing more.
Instead I had two cases in my life with hypoxia and no hypercapnia.
In both cases I was doing some extreme free diving, after minutes of strong hyperventilation, which did remove almost entirely the CO2 from my body.
In both cases I passed out, with absolutely no symptom and no feeling of needing to breath. I was just feeling fine, and wondering how nice was free diving and how long I was staying underwater...
Luckily enough other divers resuscitated me with no consequences. But I did learn the hard way that hypoxia is, at least for me, completely asyntomatic.

 

[stretchthepenn]

We call it a "Duck dive" although there may be other words for it. Standard practice in freedving.

In swimming, we call it a "pike" dive. I think it's named after the gymnastics move.