Oxygen, Lost submarines, and Scrubbing

A little over a week ago an Argentine submarine (ARA San Juan) was lost at sea and time begun to run out as the search neared its 7th day. The theory was that if the submarine had surfaced and refreshed its air supply just before the last time it was heard from on Wednesday the 21st, it would have approximately 7 to 10 days worth of air within its hull. Recent reports indicate that there was an explosion near where the submarine was last heard from before going missing.

ARA San Juan

Obviously an explosion on a submarine is not a situation that I expect to find myself in anytime soon but when I heard this story my mind immediately went to how would I survive if in a situation where air was limited or running out. Assuming I had the tools and resources I needed to construct a rebreather, would a rebreather be worth building? Would it be able to extend my total breathing time?

What is a rebreather?

Wikipedia describes a rebreather as:
A rebreather is a breathing apparatus that absorbs the carbon dioxide of a user’s exhaled breath to permit the rebreathing (recycling) of the substantially unused oxygen content, and unused inert content when present, of each breath. Oxygen is added to replenish the amount metabolised by the user. This differs from an open-circuit breathing apparatus, where the exhaled gas is discharged directly into the environment

How does this differ from a CO2 Scrubber?

A carbon dioxide scrubber is a device which absorbs carbon dioxide (CO2). It is used to treat exhaust gases from industrial plants or from exhaled air in life support systems such as rebreathers or in spacecraft, submersible craft or airtight chambers. Carbon dioxide scrubbers are also used in controlled atmosphere (CA) storage. They have also been researched for carbon capture.

Submersible craft typically have C02 Scrubbers installed within them as part of their life support systems to constantly pull the carbon dioxide out of the atmosphere. I was not able to find out if the ARA San Juan had a CO2 Scrubber but for the air in the submarine to last 10 days with the crew of 44 it would likely have needed a scrubbing unit.

A CO2 scrubber is a component of a rebreather. If the CO2 is not removed from the air being breathed it will rapidly build up in the body and cause problems. Wikipedia does a great job of describing why a rebreather can only really be an option as long as you have an additional oxygen source to supplement the exhaled oxygen. The most important line from the Wikipedia page on rebreathers and the most important line in this article is:

Continued rebreathing of the same gas will deplete the oxygen to a level which will no longer support consciousness, and eventually life, so gas containing oxygen must be added to the breathing gas to maintain the required concentration of oxygen.

This is essentially the situation that we are seeking to avoid, the loss of consciousness and or life. Regardless of removing CO2 from the air you breathe, if the air doesn’t contain oxygen, you will eventually pass out. If that situation continues, you will eventually die. How long it take to do wither depends on many factors too numerous to mention here.

Effect of C02 over time

 

Given the information listed above even if the resources were available to create a rebreather from nearly scratch it would only be effective for as long as I was able to add oxygen into the system. So, short of having an air tank handy, how would one generate oxygen? One way would be to use electrolysis to separate hydrogen from oxygen in water. While this would generate Oxygen it also creates hydrogen, a highly explosive gas. This Wikipedia page on electrolysis details how much electricity would be needed and how much of each gas would be generated. Conveniently enough this process would need water that is capable of conducting a current, salt water would be able to do just that.

Generating hydrogen and oxygen without a way to capture and separate the two would mean that you would end up breathing both into your lungs. The would not cause you a problem but hydrogen on the other hand is more dangerous.

Hydrogen isn’t poisonous, but if you should breathe pure hydrogen you could die of asphyxiation simply because you’ll be deprived of oxygen. Worse, you won’t necessarily know that you’re breathing hydrogen because it’s invisible, odorless and flavorless — much like oxygen.

So in addition to building a contraption to capture and clean exhaled gases, an oxygen generating device  would need to be built. if it also happened to generate hydrogen you would need a way to store the hydrogen without oxidizing it or causing it to explode.

Would it be possible to build all of these items form scratch? yes, would they be worth the risks to do without it being an extreme survival situation? no. the only time it would make sense to build such a device would be as a test or proof of concept and even then such an item could be potentially fatal.

The good news is that companies make cans of breathable air, for example:http://www.spareair.com/

I am not affiliated in any way with the above company and found them through a Google search, there are others as well.  Carrying a can of spare air could be a consideration for anyone that lives in areas where the air may become unbreathable for short stretches. For me however I don’t believe I’ll be adding it to my BOB any time soon. Your mileage may vary though.

 

 

References/ outside links:

http://abcnews.go.com/International/wireStory/latest-argentina-ends-rescue-aspect-submarine-search-51495471

https://auto.howstuffworks.com/fuel-efficiency/alternative-fuels/hydrogen-vehicle-danger1.htm

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