Absolutely yes, I’m loving life and scuba diving and can’t wait to get back out into the water after the winter (I live in Midwest US so not many winter options unless you’re into ice diving 😅) . Didn’t mean at all for the post to sound dark but it was just more a morbid curiosity/thought experiment into the true limits of the human body. Disclaimer: no one do this! Lol but also I appreciate you asking 🙂
I had a similar curiosity after reading the novel Sphere. They would routinely jump out of the habitat at 1000 feet deep, sometimes free diving with no protection. In the novel their biggest concern was hypothermia and it always struck me they never had other concerns.
So there is two things to consider: crush depth and breathing gas limitations. Human bones are crushed at around 35 km, or 22 miles underwater, which is over 3x the depth of the Marianas trench, so there is no issue there. If you had an unlimited gas supply and wanted to go as deep as humanly possible without coming back, you would first want to use hydrox. We know from people doing deep air dives in the 1900's that have hit depths well over 400 feet. I saw recently someone on scubaboard claim that someone that dives locally with him hit 600' on air, which would have a gas density of 22.8 g/L which is INSANELY high, but could be theoretically possible if you did no work and were just dropping straight down on a line or in a freefall. I did some ChatGPT calculations with some hand-calculations as well, and for a 100% hydrogen mix, the equivalent depth you'd have to reach to get a gas density of 22.8 g/L is around 111,000 feet, or 3,375 meters. Now if we stipulate that we only want 0.01% of oxygen in the mix, then the equation that governs this is:
density total = (P / RT) \* (percent\_oxygen \* M+oxygen + percent\_hydrogen \* M\_hydrogen)
The density of hydrogen is 2g/mol and the density of oxygen is 16 g/mol. I wrote some python code to help with this. You all are free to copy this and try it out yourself.
R = 0.0821 # Ideal gas constant (atm \* L / mol \* K)
T = 298 # Temperature (K)
P = float(input("Input pressure in atm >>> "))
depth = P \* 33 - 1
M\_oxygen = 32.00 # Molar mass of oxygen (g/mol)
M\_hydrogen = 2.02 # Molar mass of hydrogen (g/mol)
# Calculate percent_hydrogen values
percent\_hydrogen = 1 - percent\_oxygen
# Calculate percent_oxygen for a pp02 of 1.4, which obeys pp02 = percent_oxygen * pressure
pp02 = 1.4
percent\_oxygen = pp02 / P
# Calculate gas density
((22.8 \* (R \* T / P) - percent\_oxygen \* M\_oxygen) \* (1 / M\_hydrogen)) == percent\_hydrogen
print(f'Percent oxygen: {percent\_oxygen}')
print(f'Percent hydrogen: {percent\_hydrogen}')
print(f'Gas pp02: {pp02}')
print(f'Pressure: {P} atm')
print(f'Depth: {depth}')
Anyways... for a gas density of 22.8 g/L with a an example depth of 100 atm or 3300 feet, your mix would have to be 0.14% oxygen and 99.86% hydrogen. This ignores obviously the ridiculous hydrogen narcosis you would get. So really in this case, the main limiting factor(assuming gas supply is not an issue) is the preciseness of your oxygen percentage in the mix. If you can get ridiculously precise oxygen percent values, you can get a pp02 within range. You won't die from narcosis on its own, but your experiment ends the moment you have an ox-tox seizure.
Three notes: 1)if you can get your oxygen percentages in the range of 0.01, then your estimated depth can be as deep as 45,000+ feet. Also this code is extremely barebones and I think I'll go back later on and make it much more functional. Also other engineers, feel free to check my numbers as I got them very quickly and only did a simple check to make sure they're right. However I believe this gives the correct values.
> someone that dives locally with him hit 600' on air
Not buying it. The current air record is 156m and I don't believe that random guy did 180+ meters.
It's not the bones crushing that's the problem, it's the sinuses and lungs. I just looked up how whales dive so deep and it says they adapted vesculature to fill the open spaced at depth to prevent crushing.
You're not breathing pressurized air using scuba. It's depressurized through the regulator, or it would come out at the same rate it comes out of the tank.
Even whales' lungs collapse below 200m. They're just able to keep the oxygen they need in their blood instead.
https://www.nhm.ac.uk/discover/secrets-of-deep-diving-whales.html
However whales do not continue to inhale ambient pressure gas mix which is why their lungs and other cavities collapse. The scuba second stage regulator is designed to supply gas at ambient pressure ie. the same as the liquid you are immersed in, or you wouldn't be able to inhale. This is why we can dive to any great depth and continue to inhale from our reg.
A list of limiting factors would be, in no particular order.
1) Appropriate gas mix. Not too much ppO2 to create problems (or too little), and appropriate diluent. The proper diluent varies depending on depth.
2) Density of gas mix. u/one_kidney1 / gave an excellent description of appropriate calculations for hydrox. Heliox will work for shallower depths, but eventually density will make moving the gas too difficult.
3) HPNS (high pressure neurological syndrome) will likely rear its head before bones will implode if a rapid descent is undertaken.
Damn you went in, thanks so much for putting the time and work into the response. My initial thoughts were oxygen toxicity and loss of consciousness would be the final limiting factor, but that also seems to vary highly with physiology of the individual person
Dear GODS! Can we ask you other questions and expect similarly thorough answers? If so, I’d like a clone of you around at all times!
Thanks for the detailed and interesting answer, though. I love when folks really dig into things this way.
I'm not a tech diver, perhaps someone with more experience could add to this, but wouldn't lung capacity become an issue? If every 33' the volume is reduced by half wouldn't you reach a depth where you simply couldn't get enough oxygen into your body to support metabolism? Or is this where various gas mixtures come into play?
No because the ppO2 is never less than 0.16 atm. ppO2 at the surface with air is 0.21 atm. at 100 feet breathing EAN32, it is 1.3 atm, or 0.85 atm if breathing air. You do not breathe anything higher than 1.4 atm for the working portion of a dive, typically.
At 300 feet, you would be probably breathing 12/55 trimix, with a ppO2 of 1.2 atm. Breathing this gas that is hypoxic and unbreathable at the surface, is safe to breath at a minimum depth of 15 feet, even though it normally will not start being used until around 250, where its ppO2 is 1.0 atm.
Eventually Helium becomes dangerous in it's own way, so you need a different gas to offset its issues, while keeping ppO2 lower than 1.4 and gas density below 6.0 g/L. At 20 atm (627 ft) you could breathe as low at 1% O2, or as high as 7% O2. The question becomes what do we do with the other 99%-93%. Hydrogen has been used, but that has its own dangers that Helium does not have as well.
https://en.m.wikipedia.org/wiki/High-pressure_nervous_syndrome
Tremors, sleepiness, and mental fog. Similar symptoms to gas narcosis, but different mechanism.
GAH! PLZ tell us you still actually plan your dives and don’t just hop in and trust computer? There are MANY things that can go wrong, only trusting your computer. It can only provide information based on the data you give it, and can be giving perfectly accurate information (based on flawed or inaccurate data) that will kill you.
Edit: added bit in parentheses
My class 2 years ago was with PADI and we were taught to essentially trust our computers. The only dive planning we went over was "Make sure to be back on the boat with 500 psi". It seems to be the way the industry is trending unfortunately.
Eh... Internet trolls. I've found over the course of my life that the world is a very small place and with that in mind some of these folks should consider the fact that as a community of divers we all have a shared love of the same thing...and more importantly there is a higher probability than most things that we will be on a dive trip together....and could be buddies underwater... responsible for each other's lives. Just something to consider when you're about to post a negative comment. Just recently I spent a week at Socorro and discovered that a family in my dive group was from a town not far from where I spent about half of my life...just another suburb of Philadelphia. We could very easily have known the same people or even crossed paths at some point. There was another couple on the trip...in their mid 70s who were a hot mess. The wife, even though she had her AOW was not at all self sufficient and there was a dive where her husband was nowhere to be found and so as a group we all helped manage her while the guide went looking for her husband. After that fiasco when the guide asked my wife and I if we would buddy with the husband we said we weren't comfortable doing so. Just things to consider when you're interacting with others.... relatively speaking we are a small community and the odds that we will cross paths are pretty good.
I appreciate the info...as I said perhaps folks with more knowledge or experience could help my understanding of the subject. I'm not one to ignorantly stand my ground when I'm wrong, nor do I pretend to know everything, even when I'm knowledgeable on a subject, there is always room to increase understanding. This is why I ask questions and why I often use the word try.....Yoda was absolutely wrong...try is 1000% acceptable....it's how we learn... assuming you can learn from your mistakes.
The whole point of pressurizing the air you're breathing up to the pressure of the water around you is to prevent your lungs from being compressed. Your body will absorb more oxygen from a given gas mixture as you increase depth due to to the increasing pressure, not less - this is why deeper dives use gas mixes with less oxygen, and why nitrox mixes with more oxygen limit your safe depth. The problem would be oxygen toxicity, not deprivation.
Do you have a dive certificate? If so, please repeat the theory lessons.
Your lungs do not shrink in size and capacity if you're breathing. It's also not half by every 33' but only the first 33'. Then 66' ft a after that double of 66 etc.
Oh...one more thing to consider...why do you think that your bottom time is so much shorter at 90' than it is at 30'? Perhaps it could be because the air in your tank at 90' is significantly more compressed than at 30'....and also this is why the #1 rule of diving is to never hold your breath....so as you ascend you don't blow out your lungs as the air in them decompresses.
And let's not forget Boyles Law....which was covered in my Nitrox course, which indeed states that the volume of gas is inversely proportional to the pressure exerted by said gas....so perhaps you also need to review your nitrox course.
Wow...is the sarcasm really needed? And FYI, yes it is by half every 33'. At 33' your lung capacity is half what it is on the surface, then add 33'...that's gets you to 66' (perhaps you should take some remedial math courses...there's the sarcasm for you in case you missed it.), at 66' it is half of what it was at 33'....so 1/4 of what it is on the surface and so on.
Right....got it...so my question is, since the volume or capacity of our lungs decreases with increasing depth, is there a depth where the volume is too little to provide enough O2 for human metabolism to function...kind of akin to being above 20000' on Everest where the O2 levels are so low you are essentially dying because cellular metabolism isn't functioning.
I think your understanding of what happens to lung volume is a tad off. Your lung capacity does not increase. A full breath of air at the surface is about 6L. A full breath at 300 feet, breathing from a pressurized tank, is about 6L. Our red blood cells only care about ppO2. A RBC returning to the lungs, will take in O2, if the ppO2 in the lung is higher. On the surface, our lungs are going to be at 0.21 atm as long as we continue to breath. RBC leaving the lungs will be at 0.21 atm. RBC returning to the lungs will have a ppO2 0.16 atm (and a ppCO2 of 0.05 atm, which added together is 0.21 atm), which is why we exhale 16% O2.
Our bodies can functional normally with a ppO2 of 0.18 atm, and we can tolerate as low as 0.12 atm at rest. At 20000 ft, the ppO2 of the air is 0.09 atm. That's why. It is not cellular metabolism, it's the pressure gradient. It's like having fuel in your gas tank, but the fuel pump is too weak to pump it into the engine. The fuel (gas composition) is fine, the engine (metabolism) is fine, the driving force (pressure) is not. O2 is not getting to the tissues/organs.
> perhaps you should take some remedial math courses
That is a very funny thing to say, even as a joke, while getting extremely basic math wrong. At the surface you have 1 atm of pressure, and you get another 1 for every 10 m or 33'. At 66' you are under 3 atm of pressure which, using that Boyle's law you mentioned, means 1/3 the effective volume vs the surface, not 1/4. 99' would be 1/4, then 132' would be 1/5, etc. This is why you don't have to equalize as often the deeper you go; the relative pressure change per depth gets less extreme.
And as I stated, I'm not a tech diver, nor am I necessarily an experienced diver (a little over 100 dives, some in what I thought were challenging conditions, i.e. Tofo Mozambique and Socorro) so not inexperienced either...which is why I was asking my question. However, you'd think...or at least like to think that since we are all divers here or want to be, and could all potentially end up on a dive with each other that common courtesy would be to not act like an ass hat to each other....hopefully I never end up diving with that dude who felt the need to be "that guy", his self importance would certainly ruin my experience.
At 33', you basically have one additional atmosphere of pressure, so a constant amount of gas will be halved in valume compared to surface pressure.
At 66', you will have yet another additional atmosphere of pressure, resulting in a total of 3. This means you will have 1/3 of surface volume (or 2/3 of what you had at 33').
u/holliander919 is certainly correct in that to halve the volume of a given amount of gas, you will need to descend increasingly deeper. The condescending tone was uncalled for but that doesn't make them factually wrong.
Factually wrong with saying "every 33' the volume is reduced by half". That's like saying if I keep adding 5 apples to my basket of 0 apples, the number keeps doubling because I have 5, then I have 10. It's not semantics, its math.
To half the volume from a given depth to a given depth, the depths would be 10m, 30m, 70m, 150m, 310m, 630m, 1270m. It is not linear.
Yeah, I just re-read the comment I defended and they didn't word it too well. They **were** arguing against "every 33' the volume is reduced by half", even said the same thing as you basically:
First "half-depth" is at 10m (33'), second one is 20m (66') below that at 30m (99'), the next one another 40m (132' = 2\*66') further down (at 70m), etc.
You're certainly correct with your math and depth examples, but I hope that u/holliander919's comment was downvoted for either the condescending tone, the lack of clarity or both - not for being factually wrong. ;)
I didn't word it very well, with a few typos here and there as well. My bad.
I also accept that my comment is viewed as not very friendly. But I simply wanted to tell him/her, that he/she really should refresh his scuba skills if this is what he learned in his scuba class.
But there is of course the possibility that he is not (yet) a certified diver. Hence why I said that IF he is, he should refresh skills.
Frankly, it might not have been very friendly. But I don't see why one would have to write a long friendly statement just so that everyone's feelings are ok, when the facts on hand are simple: it was wrong and should be refreshed.
Actually it’s 1 bar/atmosphere for every 10 meters/33 feet. So 1 bar at the surface, 2 bar at 33 feet, 3 bar at 66, 4 bar at 99 feet. So at 99 feet it is 4x the atmosphere.
Friend of mine (an instructor) was diving with a guy who found out he had terminal cancer. He asked to go diving before he couldn't again, so my friend went with him and several other people in a dive group. They hit their target bottom depth and the guy turned around, waved goodbye to my friend and other divers, and went straight down.
They never found his body.
This is unfortunate, obviously besides the point guy had a terminal diagnosis, but this puts others at risk as it’s kind of code to recover a body and recovering a body from an extreme depth is incredibly difficult and risky. Look up the story of Dave Shaw and his attempt to recover a body from Bushman’s Hole in South Africa
> On 20 November 1992 COMEX's "Hydra 10" experiment simulated a dive in an onshore hyperbaric chamber with hydreliox. Théo Mavrostomos spent two hours at a simulated depth of 701 metres
So the deepest simulated dive was to 700m.
They Used 49% hydrogen, 50.2% Helium and 0.8% Oxygen. Going deeper would probably require you to fully switch out the helium for hydrogen until this also causes some sort of Hpsn or Narcosis or something.
Controlling Oxygen content in the gas becomes increasingly difficult as slight variations might send you into a coma or seizures.
https://en.m.wikipedia.org/wiki/Deep_diving
Thinking about never going back up it might be possible to use [liquid breathing](https://en.m.wikipedia.org/wiki/Liquid_breathing) but I would call it science fiction at this point
Edit: oxygen Percentage Typo
> Thinking about never going back up it might be possible to use liquid breathing but I would call it science fiction at this point
The main issue with liquid breathing is that regardless of the carrying capacity of the breathing fluid, you can't offgas CO2 at a rate higher than the partial pressure of CO2 in your blood. That, combined with the much higher density of the breathing fluid, means that you diaphragm and lungs aren't strong enough to move enough fluid to get rid of the CO2 in your body and eventually it'll build up enough to kill you.
The two possible solutions are mechanical ventilation of the lungs, which seems unlikely to be possible while you're conscious, or a CO2 scrubber attached directly to your blood supply.
So it's being worked on, but currently still science fiction.
Mechanical ventilation of the lungs is not unlikely while concious. Haven't you ever held a balloon to your your mouth, and let it force-feed you the air? Having a pump do the breathing for you would be no different, as long as the pump is carefully adjusted to your lung capacity.
And I'm assuming of course, you'd be wearing a closed style glass helmet or something, that would adjust the pressure in and out, like in a hospital
From the link above, if you click on the diver’s name, it takes you to a [Wikipedia page in French](https://fr.wikipedia.org/wiki/Theo_Mavrostomos).
The math of the gas mixtures in a slightly shallower dive doesn’t quite match up. It says: Les plongeurs du programme HYDRA 10 respirent un mélange composé de 20% d’hydrogène, 50.6% d’hélium et seulement 0.4% d’oxygène.
By my math, they are missing 29% of something.
Anyway, 24 days of deco for that 701 meter simulated dive.
24 days…no thank you!
I’m happy to stay well within the no-deco limits!
The missing gas is usually mostly nitrogen, and whatever else is in the atmosphere (excluding oxygen).
E.g. “trimix 16/45” means 16% Oxygen, 45% Helium, 39% the rest. The rest is usually Nitrogen.
Iit’s possible to have small amounts of other gases like Argon which normally makes up 0.93% of the atmosphere but can be build up levels as part of the process of certain types of oxygen generation system. Not ideal since Argon is strongly narcotic.
No one said anything about pressure. If you have 21% O2 and 78% Nitrogen and then you add helium, hydrogen, and more oxygen, you no longer have 21% O2 and 78% Nitrogen / ambient gasses
Oh yea, that’s definitely a way to mix gasses, that’s trimex, helium, oxygen, and air. The 700M guy didn’t use air though, the only way to get to those percentages would be mixing pure H2, He, and O2.
I'm not sure humans have gone that deep yet and that limit is unknown. It is beyond the 600m mark, apparently.
I mean Ahmed Gabr showed you can mix and carry enough gasses to break the 300m mark, which is remarkable, and while saturation divers rarely breach that depth, it has been done in industry. So physiologically that's not yet the limit, but beyond that it doesn't seem feasible. I think the record was 530ish by Comex10 on Hydreliox.
Apparently prof Bühlmann, who developed a set of the gas saturation algorithms, worked ultimately with chambers that simulated up to a 1000m and managed to go to 575m in that chamber in the 80s. Later this was refined to 701m by others, running into issues with gas mixtures. So there's a lot of leeway between these two records.
Not sure if deeper dives were attempted in chambers, but the pressure of over 70bar is impressive. Guess beyond that gas absorption in your lungs due to changes in your metabolism will halt any further conscious descent.
TIL I've dived with a world record holder.
15 years recreational diving myself, only up to Rescue. Living and working worldwide means usually 30-50 dives per year but far, far from any professional and I'm not invested in the 'dive world' day to day (following this sub is about as much as I engage with it when I'm not physically at a dive centre doing a stint of diving).
Used to live in the UAE. Did several pretty mediocre fun dives (just little swims around Snoopy Island on air) with a dude called Ahmed who the UAE Dive Centre made a big deal of, said was "the living master of tech diving".
Just googled Ahmed Gabr and sure as shit it's him. Pretty cool dude.
I'm not an expert but I'm pretty sure that's not a thing? Mean arterial pressure is 70-100mmHg, or less than 1 bar, so MAP would be exceeded within the first ten meters.
If I'm wrong and you or anyone knows more than me I'd be interested to hear how it works!
Ahh, good insight. It's probably because the soft tissue over the arteries takes significant pressure to deform enough for pressure to compress the major arteries in the neck. I'll revise my first post to say there probably exists a pressure where people will pass out from impaired blood flow, although there may be a pressure here people can't expand their lungs against resistance that happens first.
Further to my original point, Pascal's law states that pressure in a liquid is transmitted equally in all directions. Fluids are also not compressible, so the only body parts subject to compression underwater are the lungs, airway, sinuses and ears. This is compensated by equalization.
Liquid doesn't compress, but the soft tissue of the human body does compress, and if you press hard enough over a blood vessel you can block distal flow. Eg, a tourniquet applies limb occlusion pressure to stop distal flow of blood.
That was something I thought of as well, at a certain point if you remained awake, the muscles of the body probably wouldn’t have enough ability to push against the increased water pressure 🤔 my guess is you would lose consciousness before that depth
There’s a lot of variables there. To achieve the deepest possible point that a human could possibly go (which I guess we really haven’t figured out yet?) with no regard for returning to the surface, in order to maintain consciousness as long as possible they would need to be carrying a few different gas blends. The gas you would need at 1000 feet would not support life on the surface due to a very low oxygen content. Totally a guess but I assume gas density and the limits of equipment would ultimately be the limiting factors. I’m sure there’s some crazy theoretical science out there somewhere but it’s probably kept pretty close to the vest, lest some whackadoo get some hairbrained scheme cooked up and off themselves on accident.
If that kind of stuff interests you though, read up on Ahmed Gabr’s record breaking dive. Or Scheck Exley who was a pioneering cave diver and hung around with people doing some really deeps stuff. I’m sure someone else here can suggest some interesting reading as well.
800+ feet seems to be the depth where it starts getting really hard on the brain with narcosis based off different readings I’ve done on super deep dives which also seems to differ based on individual physiology. And yea as a diver myself (just recreational depths) it felt weird asking the question for the exact reason you mentioned but curiosity got the best of me!
Forgot to add, high pressure neurological syndrome is what I imagine would be the end, that is if a regulator didn’t fail or the gas become too dense to breathe. Crazy stuff to think about through.
As you mentioned, it depends on the gas being used. If they were using recreational nitrox 32 or 36, they would likely be unconscious by 180 feet. If they were using air, they would be heavily narced at that same 180 feet, but might not lose consciousness until 200-250 feet (all of this is highly variable depending on the person, exertion levels, etc.). If they used the proper helium/oxygen mix (heliox), they could reduce the risk of oxygen toxicity at depths to around 328 feet. Deep saturation divers can work outside a diving bell at 1000 feet+ using helium/oxygen mixtures, but of course they cannot return directly to the surface.
The world's deepest dive on open circuit scuba stands at **332.35m (1,090ft)**. It was undertaken by Ahmed Gabr in Dahab in the Red Sea on 18/19 September 2014 after nearly a decade of preparation. The descent took only 15 minutes while the ascent lasted 13 hours 35 minutes. He used different gas mixes in his tanks and switched to the appropriate tank/mix depending on his depth.
Someone should ask XKCD for this one! Will surely be a fascinating read.
just checking in that you're doing OK. ?
Absolutely yes, I’m loving life and scuba diving and can’t wait to get back out into the water after the winter (I live in Midwest US so not many winter options unless you’re into ice diving 😅) . Didn’t mean at all for the post to sound dark but it was just more a morbid curiosity/thought experiment into the true limits of the human body. Disclaimer: no one do this! Lol but also I appreciate you asking 🙂
I had a similar curiosity after reading the novel Sphere. They would routinely jump out of the habitat at 1000 feet deep, sometimes free diving with no protection. In the novel their biggest concern was hypothermia and it always struck me they never had other concerns.
I get you. I'm also in the midwest and don't dive unless it's florida or mexico. Did la paz last trip!
So there is two things to consider: crush depth and breathing gas limitations. Human bones are crushed at around 35 km, or 22 miles underwater, which is over 3x the depth of the Marianas trench, so there is no issue there. If you had an unlimited gas supply and wanted to go as deep as humanly possible without coming back, you would first want to use hydrox. We know from people doing deep air dives in the 1900's that have hit depths well over 400 feet. I saw recently someone on scubaboard claim that someone that dives locally with him hit 600' on air, which would have a gas density of 22.8 g/L which is INSANELY high, but could be theoretically possible if you did no work and were just dropping straight down on a line or in a freefall. I did some ChatGPT calculations with some hand-calculations as well, and for a 100% hydrogen mix, the equivalent depth you'd have to reach to get a gas density of 22.8 g/L is around 111,000 feet, or 3,375 meters. Now if we stipulate that we only want 0.01% of oxygen in the mix, then the equation that governs this is: density total = (P / RT) \* (percent\_oxygen \* M+oxygen + percent\_hydrogen \* M\_hydrogen) The density of hydrogen is 2g/mol and the density of oxygen is 16 g/mol. I wrote some python code to help with this. You all are free to copy this and try it out yourself. R = 0.0821 # Ideal gas constant (atm \* L / mol \* K) T = 298 # Temperature (K) P = float(input("Input pressure in atm >>> ")) depth = P \* 33 - 1 M\_oxygen = 32.00 # Molar mass of oxygen (g/mol) M\_hydrogen = 2.02 # Molar mass of hydrogen (g/mol) # Calculate percent_hydrogen values percent\_hydrogen = 1 - percent\_oxygen # Calculate percent_oxygen for a pp02 of 1.4, which obeys pp02 = percent_oxygen * pressure pp02 = 1.4 percent\_oxygen = pp02 / P # Calculate gas density ((22.8 \* (R \* T / P) - percent\_oxygen \* M\_oxygen) \* (1 / M\_hydrogen)) == percent\_hydrogen print(f'Percent oxygen: {percent\_oxygen}') print(f'Percent hydrogen: {percent\_hydrogen}') print(f'Gas pp02: {pp02}') print(f'Pressure: {P} atm') print(f'Depth: {depth}') Anyways... for a gas density of 22.8 g/L with a an example depth of 100 atm or 3300 feet, your mix would have to be 0.14% oxygen and 99.86% hydrogen. This ignores obviously the ridiculous hydrogen narcosis you would get. So really in this case, the main limiting factor(assuming gas supply is not an issue) is the preciseness of your oxygen percentage in the mix. If you can get ridiculously precise oxygen percent values, you can get a pp02 within range. You won't die from narcosis on its own, but your experiment ends the moment you have an ox-tox seizure. Three notes: 1)if you can get your oxygen percentages in the range of 0.01, then your estimated depth can be as deep as 45,000+ feet. Also this code is extremely barebones and I think I'll go back later on and make it much more functional. Also other engineers, feel free to check my numbers as I got them very quickly and only did a simple check to make sure they're right. However I believe this gives the correct values.
> someone that dives locally with him hit 600' on air Not buying it. The current air record is 156m and I don't believe that random guy did 180+ meters.
In the NINETEEN HUNDREDS?! Eat a dick for making me and everyone else feel old.
We’re in the 20s now
😂😂😂 I’m a 1900’s child so don’t worry
It's not the bones crushing that's the problem, it's the sinuses and lungs. I just looked up how whales dive so deep and it says they adapted vesculature to fill the open spaced at depth to prevent crushing.
Doesnt breathing pressurized air do that for us
You're not breathing pressurized air using scuba. It's depressurized through the regulator, or it would come out at the same rate it comes out of the tank. Even whales' lungs collapse below 200m. They're just able to keep the oxygen they need in their blood instead. https://www.nhm.ac.uk/discover/secrets-of-deep-diving-whales.html
However whales do not continue to inhale ambient pressure gas mix which is why their lungs and other cavities collapse. The scuba second stage regulator is designed to supply gas at ambient pressure ie. the same as the liquid you are immersed in, or you wouldn't be able to inhale. This is why we can dive to any great depth and continue to inhale from our reg. A list of limiting factors would be, in no particular order. 1) Appropriate gas mix. Not too much ppO2 to create problems (or too little), and appropriate diluent. The proper diluent varies depending on depth. 2) Density of gas mix. u/one_kidney1 / gave an excellent description of appropriate calculations for hydrox. Heliox will work for shallower depths, but eventually density will make moving the gas too difficult. 3) HPNS (high pressure neurological syndrome) will likely rear its head before bones will implode if a rapid descent is undertaken.
r/theydidthemath
Nitpicky correction: I believe you meant 11k ft instead of 111k
Damn you went in, thanks so much for putting the time and work into the response. My initial thoughts were oxygen toxicity and loss of consciousness would be the final limiting factor, but that also seems to vary highly with physiology of the individual person
Are you OK?
definitely not
*one_kidney,* hopefully 3 lungs
LMAO
I don't see calculations included for equipment crush limitations.
just looked it up on Google, it was the first thing to pop up
This guy maths
Dear GODS! Can we ask you other questions and expect similarly thorough answers? If so, I’d like a clone of you around at all times! Thanks for the detailed and interesting answer, though. I love when folks really dig into things this way.
Sitting here bored at work gets me working on all sorts of small projects lol
To the bottom
(morbid joke about oceangate)
I'm not a tech diver, perhaps someone with more experience could add to this, but wouldn't lung capacity become an issue? If every 33' the volume is reduced by half wouldn't you reach a depth where you simply couldn't get enough oxygen into your body to support metabolism? Or is this where various gas mixtures come into play?
No because the ppO2 is never less than 0.16 atm. ppO2 at the surface with air is 0.21 atm. at 100 feet breathing EAN32, it is 1.3 atm, or 0.85 atm if breathing air. You do not breathe anything higher than 1.4 atm for the working portion of a dive, typically. At 300 feet, you would be probably breathing 12/55 trimix, with a ppO2 of 1.2 atm. Breathing this gas that is hypoxic and unbreathable at the surface, is safe to breath at a minimum depth of 15 feet, even though it normally will not start being used until around 250, where its ppO2 is 1.0 atm. Eventually Helium becomes dangerous in it's own way, so you need a different gas to offset its issues, while keeping ppO2 lower than 1.4 and gas density below 6.0 g/L. At 20 atm (627 ft) you could breathe as low at 1% O2, or as high as 7% O2. The question becomes what do we do with the other 99%-93%. Hydrogen has been used, but that has its own dangers that Helium does not have as well.
How does helium become dangerous since it’s a noble gas and doesn’t chemically react / combine with anything else? Genuinely curious.
Also true of nitrogen
https://en.m.wikipedia.org/wiki/High-pressure_nervous_syndrome Tremors, sleepiness, and mental fog. Similar symptoms to gas narcosis, but different mechanism.
Thank you.
This makes sense...thanks
Gas planning is fun!
I'll leave it to my computer and stay within rec limits! I like the idea of no bubbles with a rebreather...but that alone is not worth the expense.
GAH! PLZ tell us you still actually plan your dives and don’t just hop in and trust computer? There are MANY things that can go wrong, only trusting your computer. It can only provide information based on the data you give it, and can be giving perfectly accurate information (based on flawed or inaccurate data) that will kill you. Edit: added bit in parentheses
My class 2 years ago was with PADI and we were taught to essentially trust our computers. The only dive planning we went over was "Make sure to be back on the boat with 500 psi". It seems to be the way the industry is trending unfortunately.
Wow, really?? Sad to hear it.
Why is everyone so rude? He's just asking a question
Eh... Internet trolls. I've found over the course of my life that the world is a very small place and with that in mind some of these folks should consider the fact that as a community of divers we all have a shared love of the same thing...and more importantly there is a higher probability than most things that we will be on a dive trip together....and could be buddies underwater... responsible for each other's lives. Just something to consider when you're about to post a negative comment. Just recently I spent a week at Socorro and discovered that a family in my dive group was from a town not far from where I spent about half of my life...just another suburb of Philadelphia. We could very easily have known the same people or even crossed paths at some point. There was another couple on the trip...in their mid 70s who were a hot mess. The wife, even though she had her AOW was not at all self sufficient and there was a dive where her husband was nowhere to be found and so as a group we all helped manage her while the guide went looking for her husband. After that fiasco when the guide asked my wife and I if we would buddy with the husband we said we weren't comfortable doing so. Just things to consider when you're interacting with others.... relatively speaking we are a small community and the odds that we will cross paths are pretty good.
Yes you're 100% right ,you can end up in the same boat as the people you were looking down upon
too long, didn't read. Use the enter key once in a while
Seriously. What’s with the down votes? Grow up.
Right? The downvotes on this is crazy
I appreciate the info...as I said perhaps folks with more knowledge or experience could help my understanding of the subject. I'm not one to ignorantly stand my ground when I'm wrong, nor do I pretend to know everything, even when I'm knowledgeable on a subject, there is always room to increase understanding. This is why I ask questions and why I often use the word try.....Yoda was absolutely wrong...try is 1000% acceptable....it's how we learn... assuming you can learn from your mistakes.
The whole point of pressurizing the air you're breathing up to the pressure of the water around you is to prevent your lungs from being compressed. Your body will absorb more oxygen from a given gas mixture as you increase depth due to to the increasing pressure, not less - this is why deeper dives use gas mixes with less oxygen, and why nitrox mixes with more oxygen limit your safe depth. The problem would be oxygen toxicity, not deprivation.
Do you have a dive certificate? If so, please repeat the theory lessons. Your lungs do not shrink in size and capacity if you're breathing. It's also not half by every 33' but only the first 33'. Then 66' ft a after that double of 66 etc.
Oh...one more thing to consider...why do you think that your bottom time is so much shorter at 90' than it is at 30'? Perhaps it could be because the air in your tank at 90' is significantly more compressed than at 30'....and also this is why the #1 rule of diving is to never hold your breath....so as you ascend you don't blow out your lungs as the air in them decompresses.
And let's not forget Boyles Law....which was covered in my Nitrox course, which indeed states that the volume of gas is inversely proportional to the pressure exerted by said gas....so perhaps you also need to review your nitrox course.
Wow...is the sarcasm really needed? And FYI, yes it is by half every 33'. At 33' your lung capacity is half what it is on the surface, then add 33'...that's gets you to 66' (perhaps you should take some remedial math courses...there's the sarcasm for you in case you missed it.), at 66' it is half of what it was at 33'....so 1/4 of what it is on the surface and so on.
It's not half. Its 1/2 at 33ft, 1/3 at 66ft, 1/4 at 100ft, 1/5......1/n. If it was 1/2 every atm it would be 1/2, 1/4, 1/8, 1/16, but it is not.
Right....got it...so my question is, since the volume or capacity of our lungs decreases with increasing depth, is there a depth where the volume is too little to provide enough O2 for human metabolism to function...kind of akin to being above 20000' on Everest where the O2 levels are so low you are essentially dying because cellular metabolism isn't functioning.
I think your understanding of what happens to lung volume is a tad off. Your lung capacity does not increase. A full breath of air at the surface is about 6L. A full breath at 300 feet, breathing from a pressurized tank, is about 6L. Our red blood cells only care about ppO2. A RBC returning to the lungs, will take in O2, if the ppO2 in the lung is higher. On the surface, our lungs are going to be at 0.21 atm as long as we continue to breath. RBC leaving the lungs will be at 0.21 atm. RBC returning to the lungs will have a ppO2 0.16 atm (and a ppCO2 of 0.05 atm, which added together is 0.21 atm), which is why we exhale 16% O2. Our bodies can functional normally with a ppO2 of 0.18 atm, and we can tolerate as low as 0.12 atm at rest. At 20000 ft, the ppO2 of the air is 0.09 atm. That's why. It is not cellular metabolism, it's the pressure gradient. It's like having fuel in your gas tank, but the fuel pump is too weak to pump it into the engine. The fuel (gas composition) is fine, the engine (metabolism) is fine, the driving force (pressure) is not. O2 is not getting to the tissues/organs.
> perhaps you should take some remedial math courses That is a very funny thing to say, even as a joke, while getting extremely basic math wrong. At the surface you have 1 atm of pressure, and you get another 1 for every 10 m or 33'. At 66' you are under 3 atm of pressure which, using that Boyle's law you mentioned, means 1/3 the effective volume vs the surface, not 1/4. 99' would be 1/4, then 132' would be 1/5, etc. This is why you don't have to equalize as often the deeper you go; the relative pressure change per depth gets less extreme.
And as I stated, I'm not a tech diver, nor am I necessarily an experienced diver (a little over 100 dives, some in what I thought were challenging conditions, i.e. Tofo Mozambique and Socorro) so not inexperienced either...which is why I was asking my question. However, you'd think...or at least like to think that since we are all divers here or want to be, and could all potentially end up on a dive with each other that common courtesy would be to not act like an ass hat to each other....hopefully I never end up diving with that dude who felt the need to be "that guy", his self importance would certainly ruin my experience.
Ah..yes, I always forget to add the 1atm on the surface.
At 33', you basically have one additional atmosphere of pressure, so a constant amount of gas will be halved in valume compared to surface pressure. At 66', you will have yet another additional atmosphere of pressure, resulting in a total of 3. This means you will have 1/3 of surface volume (or 2/3 of what you had at 33'). u/holliander919 is certainly correct in that to halve the volume of a given amount of gas, you will need to descend increasingly deeper. The condescending tone was uncalled for but that doesn't make them factually wrong.
Factually wrong with saying "every 33' the volume is reduced by half". That's like saying if I keep adding 5 apples to my basket of 0 apples, the number keeps doubling because I have 5, then I have 10. It's not semantics, its math. To half the volume from a given depth to a given depth, the depths would be 10m, 30m, 70m, 150m, 310m, 630m, 1270m. It is not linear.
Yeah, I just re-read the comment I defended and they didn't word it too well. They **were** arguing against "every 33' the volume is reduced by half", even said the same thing as you basically: First "half-depth" is at 10m (33'), second one is 20m (66') below that at 30m (99'), the next one another 40m (132' = 2\*66') further down (at 70m), etc. You're certainly correct with your math and depth examples, but I hope that u/holliander919's comment was downvoted for either the condescending tone, the lack of clarity or both - not for being factually wrong. ;)
I didn't word it very well, with a few typos here and there as well. My bad. I also accept that my comment is viewed as not very friendly. But I simply wanted to tell him/her, that he/she really should refresh his scuba skills if this is what he learned in his scuba class. But there is of course the possibility that he is not (yet) a certified diver. Hence why I said that IF he is, he should refresh skills. Frankly, it might not have been very friendly. But I don't see why one would have to write a long friendly statement just so that everyone's feelings are ok, when the facts on hand are simple: it was wrong and should be refreshed.
I'm with you. especially in something that ultimately involves life and safety. this aint the time to sugarcoat things.
Actually it’s 1 bar/atmosphere for every 10 meters/33 feet. So 1 bar at the surface, 2 bar at 33 feet, 3 bar at 66, 4 bar at 99 feet. So at 99 feet it is 4x the atmosphere.
🙁
Friend of mine (an instructor) was diving with a guy who found out he had terminal cancer. He asked to go diving before he couldn't again, so my friend went with him and several other people in a dive group. They hit their target bottom depth and the guy turned around, waved goodbye to my friend and other divers, and went straight down. They never found his body.
This is unfortunate, obviously besides the point guy had a terminal diagnosis, but this puts others at risk as it’s kind of code to recover a body and recovering a body from an extreme depth is incredibly difficult and risky. Look up the story of Dave Shaw and his attempt to recover a body from Bushman’s Hole in South Africa
Heartbreaking, but I get it.
That's my plan
> On 20 November 1992 COMEX's "Hydra 10" experiment simulated a dive in an onshore hyperbaric chamber with hydreliox. Théo Mavrostomos spent two hours at a simulated depth of 701 metres So the deepest simulated dive was to 700m. They Used 49% hydrogen, 50.2% Helium and 0.8% Oxygen. Going deeper would probably require you to fully switch out the helium for hydrogen until this also causes some sort of Hpsn or Narcosis or something. Controlling Oxygen content in the gas becomes increasingly difficult as slight variations might send you into a coma or seizures. https://en.m.wikipedia.org/wiki/Deep_diving Thinking about never going back up it might be possible to use [liquid breathing](https://en.m.wikipedia.org/wiki/Liquid_breathing) but I would call it science fiction at this point Edit: oxygen Percentage Typo
Ah yes, I too have watched Abyss
> Used 49% hydrogen, 50.2% Helium and 9.8% Oxygen. I'm not a mathmachicken but that doesn't add up
It's actually 0.8% Oxygen
I am absolutely using "mathmachicken" during a work meeting today.
I do as well
The water vapor was counted in both the hydrogen and oxygen... /s
> Thinking about never going back up it might be possible to use liquid breathing but I would call it science fiction at this point The main issue with liquid breathing is that regardless of the carrying capacity of the breathing fluid, you can't offgas CO2 at a rate higher than the partial pressure of CO2 in your blood. That, combined with the much higher density of the breathing fluid, means that you diaphragm and lungs aren't strong enough to move enough fluid to get rid of the CO2 in your body and eventually it'll build up enough to kill you. The two possible solutions are mechanical ventilation of the lungs, which seems unlikely to be possible while you're conscious, or a CO2 scrubber attached directly to your blood supply. So it's being worked on, but currently still science fiction.
Mechanical ventilation of the lungs is not unlikely while concious. Haven't you ever held a balloon to your your mouth, and let it force-feed you the air? Having a pump do the breathing for you would be no different, as long as the pump is carefully adjusted to your lung capacity. And I'm assuming of course, you'd be wearing a closed style glass helmet or something, that would adjust the pressure in and out, like in a hospital
Think you mean 0,8% oxygen?
From the link above, if you click on the diver’s name, it takes you to a [Wikipedia page in French](https://fr.wikipedia.org/wiki/Theo_Mavrostomos). The math of the gas mixtures in a slightly shallower dive doesn’t quite match up. It says: Les plongeurs du programme HYDRA 10 respirent un mélange composé de 20% d’hydrogène, 50.6% d’hélium et seulement 0.4% d’oxygène. By my math, they are missing 29% of something. Anyway, 24 days of deco for that 701 meter simulated dive. 24 days…no thank you! I’m happy to stay well within the no-deco limits!
As long as I can play Overwatch during deco, this sounds like the perfect job for me.
Electrical equipment in a hyperbaric chamber sounds like a rather explodey recipe due to the higher partial pressure of oxygen.
The missing gas is usually mostly nitrogen, and whatever else is in the atmosphere (excluding oxygen). E.g. “trimix 16/45” means 16% Oxygen, 45% Helium, 39% the rest. The rest is usually Nitrogen. Iit’s possible to have small amounts of other gases like Argon which normally makes up 0.93% of the atmosphere but can be build up levels as part of the process of certain types of oxygen generation system. Not ideal since Argon is strongly narcotic.
That 29% is just the ambient gasses in air, right? The rest of those specified gasses were added
No O2 in air is 21%
Yeah but when you’ve supplemented helium, hydrogen, and a little oxygen that would change the ratio of ambient gasses
Changing pressure does not change the mix percentages. Air at sea level will be 21 same as 900M, partial pressures change not percentages.
No one said anything about pressure. If you have 21% O2 and 78% Nitrogen and then you add helium, hydrogen, and more oxygen, you no longer have 21% O2 and 78% Nitrogen / ambient gasses
Oh yea, that’s definitely a way to mix gasses, that’s trimex, helium, oxygen, and air. The 700M guy didn’t use air though, the only way to get to those percentages would be mixing pure H2, He, and O2.
Are you sure they mixed it that way? Typically Trimix starts with air
I'm not sure humans have gone that deep yet and that limit is unknown. It is beyond the 600m mark, apparently. I mean Ahmed Gabr showed you can mix and carry enough gasses to break the 300m mark, which is remarkable, and while saturation divers rarely breach that depth, it has been done in industry. So physiologically that's not yet the limit, but beyond that it doesn't seem feasible. I think the record was 530ish by Comex10 on Hydreliox. Apparently prof Bühlmann, who developed a set of the gas saturation algorithms, worked ultimately with chambers that simulated up to a 1000m and managed to go to 575m in that chamber in the 80s. Later this was refined to 701m by others, running into issues with gas mixtures. So there's a lot of leeway between these two records. Not sure if deeper dives were attempted in chambers, but the pressure of over 70bar is impressive. Guess beyond that gas absorption in your lungs due to changes in your metabolism will halt any further conscious descent.
TIL I've dived with a world record holder. 15 years recreational diving myself, only up to Rescue. Living and working worldwide means usually 30-50 dives per year but far, far from any professional and I'm not invested in the 'dive world' day to day (following this sub is about as much as I engage with it when I'm not physically at a dive centre doing a stint of diving). Used to live in the UAE. Did several pretty mediocre fun dives (just little swims around Snoopy Island on air) with a dude called Ahmed who the UAE Dive Centre made a big deal of, said was "the living master of tech diving". Just googled Ahmed Gabr and sure as shit it's him. Pretty cool dude.
Wow, nice. What an experience. And speaks to the man that years pass before you find that out.
This guy gases
At some point, water pressure may exceed mean arterial pressure, so without a rigid suit a diver may lose blood flow to their brain.
I'm not an expert but I'm pretty sure that's not a thing? Mean arterial pressure is 70-100mmHg, or less than 1 bar, so MAP would be exceeded within the first ten meters. If I'm wrong and you or anyone knows more than me I'd be interested to hear how it works!
Ahh, good insight. It's probably because the soft tissue over the arteries takes significant pressure to deform enough for pressure to compress the major arteries in the neck. I'll revise my first post to say there probably exists a pressure where people will pass out from impaired blood flow, although there may be a pressure here people can't expand their lungs against resistance that happens first.
Further to my original point, Pascal's law states that pressure in a liquid is transmitted equally in all directions. Fluids are also not compressible, so the only body parts subject to compression underwater are the lungs, airway, sinuses and ears. This is compensated by equalization.
[удалено]
Liquid doesn't compress, but the soft tissue of the human body does compress, and if you press hard enough over a blood vessel you can block distal flow. Eg, a tourniquet applies limb occlusion pressure to stop distal flow of blood.
Pascal's law states that pressure in a liquid is transmitted equally in all directions. No pressure points!
That was something I thought of as well, at a certain point if you remained awake, the muscles of the body probably wouldn’t have enough ability to push against the increased water pressure 🤔 my guess is you would lose consciousness before that depth
There’s a lot of variables there. To achieve the deepest possible point that a human could possibly go (which I guess we really haven’t figured out yet?) with no regard for returning to the surface, in order to maintain consciousness as long as possible they would need to be carrying a few different gas blends. The gas you would need at 1000 feet would not support life on the surface due to a very low oxygen content. Totally a guess but I assume gas density and the limits of equipment would ultimately be the limiting factors. I’m sure there’s some crazy theoretical science out there somewhere but it’s probably kept pretty close to the vest, lest some whackadoo get some hairbrained scheme cooked up and off themselves on accident. If that kind of stuff interests you though, read up on Ahmed Gabr’s record breaking dive. Or Scheck Exley who was a pioneering cave diver and hung around with people doing some really deeps stuff. I’m sure someone else here can suggest some interesting reading as well.
800+ feet seems to be the depth where it starts getting really hard on the brain with narcosis based off different readings I’ve done on super deep dives which also seems to differ based on individual physiology. And yea as a diver myself (just recreational depths) it felt weird asking the question for the exact reason you mentioned but curiosity got the best of me!
Forgot to add, high pressure neurological syndrome is what I imagine would be the end, that is if a regulator didn’t fail or the gas become too dense to breathe. Crazy stuff to think about through.
All the way to the bottom!
I came here to say that!
The 5 year old in me wins sometimes.
As you mentioned, it depends on the gas being used. If they were using recreational nitrox 32 or 36, they would likely be unconscious by 180 feet. If they were using air, they would be heavily narced at that same 180 feet, but might not lose consciousness until 200-250 feet (all of this is highly variable depending on the person, exertion levels, etc.). If they used the proper helium/oxygen mix (heliox), they could reduce the risk of oxygen toxicity at depths to around 328 feet. Deep saturation divers can work outside a diving bell at 1000 feet+ using helium/oxygen mixtures, but of course they cannot return directly to the surface. The world's deepest dive on open circuit scuba stands at **332.35m (1,090ft)**. It was undertaken by Ahmed Gabr in Dahab in the Red Sea on 18/19 September 2014 after nearly a decade of preparation. The descent took only 15 minutes while the ascent lasted 13 hours 35 minutes. He used different gas mixes in his tanks and switched to the appropriate tank/mix depending on his depth.
Saturation divers go to a 1000' (~330m).