Saturday, 18 January 2014

Breathing Water

Anyone who's done a bit of scuba diving would relish the idea of breathing underwater without having to bother with any cumbersome equipment. Bite down on a small device's mouth piece and breathe normally, while it extracts the oxygen you need from the surrounding water, as you need it. This is of course the stuff of science fiction.

Which is why a recent article in the Daily Mail sounded intriguing. It's about Jeabyun Yeon, a South Korean designer, who claims to be working on such a device. It's not even a proof of concept yet, just an idea, but the hopes is that with Triton, people will be able to breathe underwater.

Obi Wan, underwater
The pictures look great and remind me of a similar device used by Obi Wan and Qui-Gon in The Phantom Menace, although it's of course much bigger (Star Wars is sci-fi after all, and has access to better imaginary technology than our own universe can manage).

But is it actually possible? Would we ever be able to grab enough oxygen from water to satisfy our body's needs with each breath we take? I have my doubts.

We can't breathe water for many reasons: it's much denser and more viscous than air, but this wouldn't stop us from surviving in it, as there can be liquids we could breathe.

What makes water useless as an oxygen provider for us humans, is how little of it there is in there in the first place.

The amount of dissolved oxygen depends on many factors, like how well aerated the water is, the ambient temperature, the atmospheric pressure and the water's salinity. But to give you an idea, at 25 degrees Celsius, freshwater contains about 6ml of oxygen per litre, while saltwater has about 5ml. The colder the water gets, the more oxygen can dissolve in it, up to 14.6ml/l at zero degrees.

But unbearable temperatures aside, even that wouldn't cut it for us as we're used to much higher concentrations since our atmosphere is composed of 20.8% oxygen.

It doesn't mean we use all of this oxygen of course: the air we breathe out has around 16% oxygen, which means our lungs capture about a quarter of it (or 5% of the total air we breathe). Still, 5% is much higher than even 14.6ml per litre.

Cold-blooded with highly efficient gills.
How can fish survive in this? Two reasons: they're cold blooded, so they need much less oxygen than we do, and their gills are extremely efficient: they capture around 80% of the dissolved oxygen.

So could a device like Triton, the one proposed by this South Korean designer, allow us to breathe underwater?

At rest, we breathe in about half a litre of air on average. This can be a very misleading number as many factors can affect this, including our size and weight, and the slightest movement on our part will increase our oxygen requirement, but let's start with half a litre per breath.

This means that we breathe in 100ml of oxygen and take in 25ml of it (20% of 500ml is 100ml, and one quarter of 100ml is 25ml).

Being in the water, our intake would increase as we'd be swimming, and expending energy to keep warm, so I'm going to assume we'd need four times as much (in high peak activities, we can use up 6 litres of air per breath so two litres is actually a pretty conservative estimate).

This means that we'd be consuming 100ml of oxygen per breath. Let's say the dissolved oxygen level in water is 10ml/litre (a temperature somewhere between zero and 25 degrees), so we'd need to filter out 10 litres of water per breath just to grab those 100ml of oxygen we need to consume. And that's assuming Triton would be 100% efficient, and how many devices do we know that are?

Exploring the seas, the more traditional way.
This just isn't practical for such a small device. We'd need a bigger machine to collect the oxygen for us into tanks, and there goes the advantage over bulky traditional scuba diving equipment, although such a device would enable us to stay under for longer periods of time...

But then, we'd encounter another problem: we'd be breathing in 100% oxygen. Our lungs just aren't designed to cope with so much highly oxidising air, and the consequences aren't good if we breathe that for any length of time.

When we do, fluid accumulates in our lungs, their alveoli's efficiency is reduced which means we must breathe in more to get enough oxygen, we can develop chest pains, and those alveoli can even collapse. Put simply, breathing 100% oxygen at a normal pressure isn't good for us. 

Reduce the pressure and the problems are alleviated, but being submerged increases that pressure, so the results could be even worse underwater: we could experience nausea, dizziness, blurred vision, seizures and convulsions... Still fancy the idea?

So sadly, such devices aren't feasible and will remain the stuff of science fiction. Sure, our technology will improve, but we can't extract more oxygen from water than is there, and our bodies are designed to need more oxygen than water can provide. No matter how advanced our technology gets, we're still limited by the confines of our own biochemistry.

We're land-dwelling mammals, and if we want to survive underwater, it looks like we'll always need to take the air we breathe with us.

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