# Breathing underwater

## Main Question or Discussion Point

So Im in highschool, so im not the smartest. That is why I have came here. I was on Kickstarter and saw a underwater drone and I got to thinking, what if we could breathe underwater. So obviously we cant take oxygen from H2O, so what if I made a giant vape type machine? What happens if you have a intake of water, some burners to create steam to breathe, and put it all in a mask sort of like a gasmask but with burners. But my big problem is that you cannot breathe in straight oxygen, but you need oxygen to breathe, BUT you CAN breathe steam, so it would take in water, create steam, you breathe it in and exhale it. I have no clue if this would work, but as a 10th grader in highschool, this could change my whole life if I found a way for this to actually work. I have to go right now but will edit this more later, please comment.

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russ_watters
Mentor
Welcome to PF!

Unfortunately, while it doesn't hurt you to inhale water vapor (not steam; that's hot), you need to be breathing free oxygen. So you can't just breathe water vapor. Water can be split into hydrogen and oxygen using electricity though. I believe that's how it's manufactured on submarines.

Keep dreaming and learning though - eventually you may invent something important!

Breathing live steam sounds like a good way to drown and internally roast one's self at the same time.

However, to your goal of apparatus that provides for advanced and efficient forms of underwater breathing, there is technology that addresses this issue. Have a look at what is known as a rebreather:

https://en.wikipedia.org/wiki/Rebreather

In one form or another, rebreathers have been around for a while, but the technology and engineering have continued to improve and develop. It is a pretty interesting area and has garnered a lot of attention and applied thought over time.

diogenesNY

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Borek
Mentor
Actually you can breath pure oxygen, although it should be not used below 10 meters depth.

russ_watters
Mentor
I should probably expand on this part, because it is quite simplified:
Unfortunately, while it doesn't hurt you to inhale water vapor (not steam; that's hot)...
You did use the word "steam" correctly and steam is a subset of "vapor"...

Steam is pure water vapor, as opposed to water vapor mixed with air or other gases.

"Steam" at atmospheric pressure is hot, but you could have steam at a lower temperature and pressure (but not under water, where the pressure needs to be higher). I'm not sure though if there is a combination of temperature and pressure where you could plausibly inhale steam and have it not be harmful. At 40C, steam's maximum pressure (saturation pressure) is is only 0.1 atmospheres. By comparison, the Apollo lunar module was pressurized to 0.3 atm.

Either way, even if the water vapor/steam didn't kill you directly, the lack of breathable oxygen would.

CWatters
Homework Helper
Gold Member
One possible option would be to use electrolysis to split water into Hydrogen and Oxygen. I don't know if you could breathe the mixture but you could seperate out the hydrogen and just breathe the Oxygen.

With some research you could find out the rate at which a diver would consume oxygen. That would allow you to calculate the amount of electrical power needed to split the water and ultimately the capacity and physical size of the battery needed for a particular duration of dive.

I haven't done the sums but I suspect the size of the battery needed might be impractical.

Edit: It seems you can breathe the mixture of hydrogen an oxygen but there are issues...

https://en.m.wikipedia.org/wiki/Hydrox_(breathing_gas)

Borek
Mentor
I haven't done the sums but I suspect the size of the battery needed might be impractical.
This. It takes a lot of energy to electrolyze water.

OmCheeto
Gold Member
This. It takes a lot of energy to electrolyze water.
Odd. We did some calculations on this a couple of years ago, and the lowest we got was 2800 watts.
Today, I did some research based on 3 independent sources, and came up with an average of 220 watts to supply one resting person with O2.
I'm fairly certain the current "order of magnitude" disparity is due to Anorlunda using an O2 consumption rate that was much higher than what I just used.

A normal minute volume while resting is about 5–8 liters per minute in humans.
Minute ventilation during moderate exercise may be between 40 and 60 litres per minute.

So 50 liters of air per minute is...
My number looks more like the 5-8 l/min.

references:
http://www.jamesoberg.com/elektron2_tec.html
This ‘Elektron-V’ system could produce up to 1900 liters [of O2] per day, with an average power load of 860 watts. [This is the device they use on the ISS]​
http://www.cres.gr/kape/publications/papers/dimosieyseis/ydrogen/A REVIEW ON WATER ELECTROLYSIS.pdf
Electrolysis plants with normal or slightly elevated pressure usually operate at electrolyte temperature of 70-90°C, cell voltage of 1.85-2.05 V and consume 4-5 KWh / m^3 of hydrogen​
https://www.hydrogen.energy.gov/pdfs/46676.pdf
4.1.4
Energy Efficiency
Based on information provided by electrolyzer suppliers for their state-of-the art technologies,
both alkaline and PEM electrolyzers are now capable of producing hydrogen using less than 50 kWh/kg​
https://health.howstuffworks.com/human-body/systems/respiratory/question98.htm
...a human being uses about 550 liters of pure oxygen (19 cubic feet) per day.​

Borek
Mentor
We are talking about diving, so the oxygen usage will be much higher than the average.

Hi, I want to thank you for helping me out on this, I shouldn't have over dramatized that title as much as I did. I did research, and pure oxygen has harmful effects, there are 3 flaws in my idea. 1 is you can't breathe steam but you can split water into oxygen, and hydrogen molecules, but I found that just breathing this can also be harmful, so I need to find out what is in our atmosphere/air since it's not put oxygen, I know there is carbon dioxide but that doesn't help us in this situation,

It is a lot easier and cheaper (energy-wise) to scrub the oxygen out of carbon dioxide than to split water. This can be done chemically and is the basis for some rebreathing technology, as well as some submarine and spacecraft atmosphere maintenance.

Revisit the rebreather link and also look up how submarines and space stations/craft maintain their breathable atmosphere. I think you will find it interesting and informative.

diogenesNY

Ive went to the link and re-breathers work well but the problem is that it uses a tank, all a re-breather does is let you use oxygen more than once, and increases the amount of time you can breathe underwater, but I want to utilize the oxygen in the water so its pretty limitless the problem is that I need to find a way to take the oxygen, and mix t with other gasses, because you cannot use the pure oxygen you obtain from the process.

Borek
Mentor
I want to utilize the oxygen in the water so its pretty limitless
It is not - you are limited by the amount of energy available to split water.

berkeman
Mentor
but I want to utilize the oxygen in the water so its pretty limitless
Then the nuclear submarine is your best model...

OmCheeto
Gold Member
We are talking about diving, so the oxygen usage will be much higher than the average.
Being a mostly sedate snorkeler, and haven't ever scuba dived, I don't know of such things.
But wiki, via the Rubicon Foundation, via the US Navy, gave me some more numbers to work with:

An average diver with a fully closed-circuit rebreather needs 1.5 liters of oxygen per minute while swimming or .64 liters per minute while resting.

O2 consumption while scuba diving
1.5 l/min swimming
3.9 times my rate [860 watts via electrolysis]​
0.64 l/min resting
1.7 times my rate [370 watts]​

I would call that "a bit higher", rather than "much" higher.

Not sure why I didn't go there first. Interesting numbers:

As a person breathes, the body consumes oxygen and produces carbon dioxide. Base metabolism requires about 0.25 L/min of oxygen from a breathing rate of about 6 L/min, and a fit person working hard may ventilate at a rate of 95 L/min but will only metabolise about 4 L/min of oxygen

O2 consumption while scuba diving
0.25 l/min base metabolic
only 65% of my base rate! [140 watts]​
4.0 l/min working hard
10 times my base rate [2300 watts]
Not sure why people work so hard when they're scuba diving. Are they chasing Black Marlins [80 mph!]?
The only time my metabolic rate went up while snorkeling was when a Moray Eel came up from the depths to greet me. (Hanauma Bay, HI. circa 1980)

all a re-breather does is let you use oxygen more than once, and increases the amount of time you can breathe underwater, but I want to utilize the oxygen in the water
Like "Artificial Gills"?
That's actually been discussed before:
Underwater Breathing Device Has $820,000 Of Funding Despite Being Scientifically Impossible Firstly, this device isn’t particularly big. In fact, it’s only 29 centimeters (11.5 inches) long. In order to filter out enough oxygen from the water for the user to, you know, not die, a device of this size would have to be getting through 90 liters (24 gallons) of water every single minute, while operating at 100 percent efficiency. That’s about six garden hoses’ worth of pressure. The only way to do this would be to have the swimmer move at speeds that would make Usain Bolt blush. Subsequent research indicates that those goof knuckles gave back the$900,000 they eventually collected from the crowd of goofier knuckles that gave them the money.

I doubt I will get any argument that "recycled" oxygen is no different than "fresh" oxygen, atomically, or diatomically speaking.
Utilizing the oxygen in the water, for your purpose, would require some very big gills, IMHO.

sophiecentaur
Gold Member
For Haemoglobin to work (absorb O2, it needs a partial pressure of around 0.2 Bar. To 'breathe' with a liquid medium, it would be necessary for sufficient Oxygen to be dissolved so that the partial pressure would be similar. Are there any non-toxic liquids that could achieve this (or even toxic ones)? The only liquid that I could think of would be Blood. What happens in the Placenta is similar but involves a different form of Haemoglobin molecule (foetal haemoglobin).
But supplying this external oxygen rich haemoglobin would involve the same sort of energy as producing gaseous oxygen in the first place - without the need for major physiological conversion surgery.

Borek
Mentor
Borek
Mentor
It is a rather poorly written piece - first, it makes a general claim that oxygen will kill you, then it explains that it will kill you only if the pressure is too high and the usage prolonged.

Pure oxygen based diving gear was (and is) used for diving as it is rarely used for longer than an hour or two. You can safely breath pure oxygen for many days, as long as its pressure is at 0.2 atm (that of a partial pressure of oxygen in the air). That's what NASA was successfully doing in their lunar missions.

LURCH
A rebreather allows O2 to be reused so that a small supply can last a long time, but not forever. Does anyone know how quickly the O2 from a tank is used up by the average diver using a rebreather? Or how much O2 could be produced by an electrolysis device powered by the swimmers own motion (breathing and swimming)? If the latter is greater than the former, then an indefinite underwater presence becomes possible. Like a nuclear sub, the only limits will be how long the diver can go without coming up for food (or water, if needed). Or sleep, of course.

Borek
Mentor
Or how much O2 could be produced by an electrolysis device powered by the swimmers own motion (breathing and swimming)?
Om's post above already contains data showing it wont work - you need at least several hundreds watts to produce enough oxygen, that's a lot.

You can safely breath pure oxygen for many days, as long as its pressure is at 0.2 atm (that of a partial pressure of oxygen in the air). That's what NASA was successfully doing in their lunar missions.
Just don't ground test at 1 atmosphere.

Borek
Mentor
Just don't ground test at 1 atmosphere.
Yes, but that's quite another issue.

epenguin
Homework Helper
Gold Member
what if we could breathe underwater. So obviously we cant take oxygen from H2O,
Actually, obviously, you ought to be able to because that is what fish and all other aquatic animals (except for 'returners' like dolphins,turtles etc) do. Just not from H2O but from the O2 dissolved in H2O. The purpose of respiration is to deliver oxygen to the tissues where it is oxidised in energy-yielding processes. In advanced active animals like fish or humans, the oxygen is delivered via a circulatory system, the oxygen being carried by the respiratory protein haemoglobin in the arteries and capillaries. You could say that the tissues don't care where the oxygen came from, so you can be kept alive without using your lungs by an artificial oxygenator in e.g. cardio pulmonary bypass surgery. As you now probably remember the oxygen is acquired from the water by diffusing into organs - gillls - that have a large surface area. While we land vertebrates get it from the air - though it still has essentially to dissolve in water, the mucus layer lining the lungs before it gets to the haemoglobin. Note that the surface area of the lung interface with air is large, of the order of the area of a tennis court, achieved by its fine branching structure.

Maybe with some such artificial branching structure and liquid-filled lungs with oxygen carrying substances like those mentioned in Borek's link, you could work out a way we could become fish. But if you only want to get from the water gaseous oxygen that we could then breathe in the normal way, fish have also part of that mechanism too. The oxygen bound to one of their haemoglobins can be released by small increase of acidity presumably ultimately under nervous control into the swim bladder organ against a high oxygen pressure gradient, by which means they control theif buoyancy. So oxygen taken from the water by one engineered device can be released in another place by another device under control of some influence like acidity, but it doesn't have to be that it could be some other soluble substance.

I saw a movie or video once (I forgot the title and details) where the man's lungs were filled up with special liquid so he could breath deep underwater in conjunction with oxygen.. is there by chance this is based on real technique or is it all fiction?