Scuba Nitrox Incident for Analysis
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OTF
Coney Island Whitefish Biologist
Oxygen is just about as narcotic as nitrogen so replacing one with the other is a wash in terms of narc.
GF99/99
Contributor
The human brain is a very powerful thing. It is amazing what we can talk our selfies into both good and bad. And once it starts its amazing how something very little can snowball into something huge. For example I am sure we have all hand that moment where your sitting in bed and you starting thinking your itchy and then be for you know it your have actually convinced your self your itchy and scratching your arm or leg a couple times over a course of 5-10 minutes even though there is absolutely nothing wrong with your arm or leg.
To me this sounds like someone just had a slight panic attack or hyperventilation since the problem resolved it self when he shallowed up and then he was able to go back down and continue diving. If there truly was a problem with his gas then he would not have been able to continue the dive and his condition would have worsened.
The fact that nitrox was involved physically is irrelevant to the incident but mentally it may have played a big role. The diver may have convinced them self there mix was bad and they were not getting enough oxygen because he was diving nitrox, or that some kind of mind trick like this. But in reality this is not physically possible.
Now he talked about gas separation so lets think about how Nitrox is made; most places use a nitrox stick or partial pressure blending and occasionally you get the membrane system. Obviously with the nitrox stick or membrane your getting the 36% mix pressurized into the tank so it would have to be 36% so this is out of the question. That leaves partial pressure blending which in theory could occur but still this is completely irrelevant because they top up with air. So lets say the shop fills an empty tank with the pure O2 need for a 36% mix then guess what the next step is to top up with AIR!. So if for some magical reason the O2 stayed at the bottom of the tank and the air on the top you will still have air on the top of the tank even though when you top up with a compressor it violently forces air into the tank which would cause it to mix, but lets say they topped with a booster at a very slow rate and then very carefully carried the tank to the customer, then he very carefully setup his gear and they were shore diving so there was no bumpy boat ride to shake the tank, then carefully entered the water geared up keeping the tank completely vertical and dropped down to 23m completely vertical guess what the "separated gas" he would be breathing is air (21%) so it physically impossible for him not to have enough oxygen even if you could somehow magically keep the nitrox mix separated in the tank. Hence why he was fine and continue the dive. Now yes I know someone is going to jump in and say yes gases do separate and yes I do know this, when I make 80% and top up with air with a booster if I don't shake/roll the tank a couple times it analyzes at about 70% but that is besides the point. Its the fact that if this magically stayed separated its still breathable 21% air that would be on the top.
Now lets really say the shop totally screwed up and they some how topped up with helium or argon instead of air which you would have to be the worlds worst gas blender to do but let just say it happened. If this was they case if my math is correct he would still have a 23/77 mix meaning there is still 23% O2 in the mix so still physically impossible to not have enough O2. Plus on surface he would have noticed right away his mix was funny if he really did have a 23/77. With that much He your second stage acts very different the gas just kind of "whips out" when you breath and during his buddy check he would of have major helium voice. Now if it was a 23/77 with argon that's a different story and I don't know what would happen then. But in theory he still could not be short on O2.
My thoughts might be wrong but to me this is not a Nitrox incident is purely a mental head game. The fact that he was on nitrox and "felt a lack of O2" is the only reason why this called a nitrox incident but in reality its not possible and this could of happened with normal air and then it just would have been called a hyperventilation/small panic attack/breathing incident.
To me this sounds like someone just had a slight panic attack or hyperventilation since the problem resolved it self when he shallowed up and then he was able to go back down and continue diving. If there truly was a problem with his gas then he would not have been able to continue the dive and his condition would have worsened.
The fact that nitrox was involved physically is irrelevant to the incident but mentally it may have played a big role. The diver may have convinced them self there mix was bad and they were not getting enough oxygen because he was diving nitrox, or that some kind of mind trick like this. But in reality this is not physically possible.
Now he talked about gas separation so lets think about how Nitrox is made; most places use a nitrox stick or partial pressure blending and occasionally you get the membrane system. Obviously with the nitrox stick or membrane your getting the 36% mix pressurized into the tank so it would have to be 36% so this is out of the question. That leaves partial pressure blending which in theory could occur but still this is completely irrelevant because they top up with air. So lets say the shop fills an empty tank with the pure O2 need for a 36% mix then guess what the next step is to top up with AIR!. So if for some magical reason the O2 stayed at the bottom of the tank and the air on the top you will still have air on the top of the tank even though when you top up with a compressor it violently forces air into the tank which would cause it to mix, but lets say they topped with a booster at a very slow rate and then very carefully carried the tank to the customer, then he very carefully setup his gear and they were shore diving so there was no bumpy boat ride to shake the tank, then carefully entered the water geared up keeping the tank completely vertical and dropped down to 23m completely vertical guess what the "separated gas" he would be breathing is air (21%) so it physically impossible for him not to have enough oxygen even if you could somehow magically keep the nitrox mix separated in the tank. Hence why he was fine and continue the dive. Now yes I know someone is going to jump in and say yes gases do separate and yes I do know this, when I make 80% and top up with air with a booster if I don't shake/roll the tank a couple times it analyzes at about 70% but that is besides the point. Its the fact that if this magically stayed separated its still breathable 21% air that would be on the top.
Now lets really say the shop totally screwed up and they some how topped up with helium or argon instead of air which you would have to be the worlds worst gas blender to do but let just say it happened. If this was they case if my math is correct he would still have a 23/77 mix meaning there is still 23% O2 in the mix so still physically impossible to not have enough O2. Plus on surface he would have noticed right away his mix was funny if he really did have a 23/77. With that much He your second stage acts very different the gas just kind of "whips out" when you breath and during his buddy check he would of have major helium voice. Now if it was a 23/77 with argon that's a different story and I don't know what would happen then. But in theory he still could not be short on O2.
My thoughts might be wrong but to me this is not a Nitrox incident is purely a mental head game. The fact that he was on nitrox and "felt a lack of O2" is the only reason why this called a nitrox incident but in reality its not possible and this could of happened with normal air and then it just would have been called a hyperventilation/small panic attack/breathing incident.
I'm wondering the same thing. That looked like a cardiac event to me. I don't want to hijack the thread, but @John C. Ratliff maybe you could make another post.
GF99/99
Contributor
Most sources say the narcosis is related to lipid solubility, not to molecular weight.
OTF
Coney Island Whitefish Biologist
And now we're getting into the realm of medical mysteries and bleeding edge research on the still very poorly understood mechanism of narcosis and anesthetics. Yup, we really don't know how anesthetics work. I can't wait to see some breakthroughs in that space, there are potentially huge gains to be made in safety for diving, surgery, and pain management.
Yep. No "medical mysteries" at play here.
Also, second a CO2 hit. Probably due to inefficient breathing plus the current that was mentioned. Exacerbated by the "dash" that he made which built up even more CO2. Oxygen starving is a sign that you're not venting enough CO2, doesn't have anything to do with O2. Oxygen is denser than nitrogen, so the gas density is actually going to be higher on rich blends vs lean. Not by much granted, but not better. 4.3g/l on 36% at 75fsw vs 4.2g/l on air at 75fsw. Gas density plays a large role in hypercapnia/CO2 hits.
It's commonly known that excess CO2 leads to panic attacks, and not the other way around. CO2 leads to a fight or flight response in our body, so the idea that people just "freak out" or "panic" is like saying people with severe depression are just "sad". There's a physiological response that overrides your psychological conditioning. It's also commonly known that CO2 sensitivity in people is highly variable so people who generally have more panic-type responses underwater aren't necessarily psychologically different than anyone else, their body just has a lower threshold for CO2 tolerance.
OTF
Coney Island Whitefish Biologist
"it seems to correlate with lipid solubility" is a far cry from "we fully understand this mechanism and there are no mysteries at play". If I'm mistaken on the current state of research (being just a dumb diver not a doctor) I'd really appreciate a proper explanation of the biochemistry involved.
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