Misdesign

The internet is a funny place. Things go “viral”: All of a sudden, ideas get an amount of attention they would otherwise not have gotten. Sometimes, that’s good: clever ideas spread much faster than they could have only a few decades ago. Sometimes, though, very half- or un-baked “ideas” make their rounds, and cause really quite unwarranted enthusiasm.

This week, I’ve seen a new “design” for a piece of diving equipment go viral. The designer came up with the “concept”, after he was frustrated by the amount of gear necessary for diving in in the real world. In short, it’s a mask plus a battery powered device extracting – breathable – oxygen from water.

Let us ignore for the moment the low originality – Obi Wan Kenobi and James Bond have already used similar gadgets – and think about how realistic such a device would be. Some back-of-the-envelope calculations will suffice:

Problem 1: It would be impossible to bring enough energy in such a small device for the extraction to work.

Seawater contains about 7 ppm (parts per million) of oxygen. That means, for each million water molecules, there are 7 oxygens. Each liter of water contains about 55 mols of water molecules. A mol is a standardized, very large number of molecules (6.022 10²³, to be exact). Hence, it contains ~0.0004 mols of dissolved oxygen (55 moles x 7 10^-6, the oxygen concentration).

A mol of gas at room temperature and surface pressure makes up 22.4 litres. Hence, to extract a liter of oxygen, one would have to harvest 1/22.4 ~= 0.04 mols of oxygen. Since each litre of seawater contains about 0.0004 mols, and we need 0.04 mols, we have to process ~ 100 litres of seawater to get 1 litre of breathable oxygen, which would sustain our diver for about a minute. Ugh.

How much energy the oxygen extraction would exactly need is hard to calculate, since it is a combination of pumping all this water through the mechanism, and the actual extraction. But certainly & common-sensically, a battery the size of a small soda can (like shown in the “design”) will not be enough to pump 100 litres of water per minute for very long. And that’s just the pumping, with no extraction yet taken into consideration.

A modern lithium battery can store about 1 MJ/kg (Megajoule per kilogram). Not enough.

The designer states that the device should carry “… a size 30 times smaller than current battery that can quickly charge 1,000 times faster.” Yes, and I want a purple pony with wings. Basing a design on a completely unrealistic technical element is like no design at all.

Pumping enough water over their gills for oxygen extraction is even hard for fishes, with way lower metabolic rates than humans. Some open-ocean fish die when they are prevented from constantly swimming (and hence stopping the water flow over their gills).

Problem 2: breathing pure oxygen will kill you below ~6 metres.

Now, let’s assume we could somehow miraculously solve this problem, and would be able to extract oxygen from water. Pure oxygen creates very reactive molecules called “free radicals” (there once was a left-wing student group at the University of Vienna chemistry department with the same name). These free radicals alter the fine-structure of a human’s nervous system in a nasty way, and cause seizures. Tech divers know this, and never use pure oxygen below 6 metres for decompression. The proposed device would kill any user at depths which can be comfortably reached by freediving.

One could of course dilute the oxygen with air, and make it breathable at deeper depths. Such devices exist, they are called “rebreathers” (I’d love to have one!). A rebreather is a sophisticated and relatively large diving machine, hardly what this new “design” envisages. Plus, a modern rebreather allows a diver to remain submerged for up to eight hours. By the end of such a dive one will be hungry and happy to ascend. It’s hardly necessary to extend the rebreather usage time with an additional oxygen extractor.

Conclusion: This won’t work, in principle, and should go unviral asap. It’s not due to my lack of imagination that it won’t work, but due to physics.

So: This “design” is like saying: I’d like to have a car with a combustion engine which can drive from Sydney to Perth on 1 litre of fuel, with aircon and radio on full power. For the price of 800$. Not going to happen, even if some designer boy really, really wants it. Reality is a bitch.