What exactly is a rebreather and what does it do?

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What exactly is a rebreather and what does it do?

Postby Mermaid » Wed Nov 29, 2006 6:33 pm

I have heard a lot about rebreathers and I have looked them up on the internet but I find it very hard to understand the jargon!!

If someone could spell it out to me so I can make sense of what they're actually for, I would appreciate it!!!

Thanks, Anna :D .
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Postby Packhorse » Wed Nov 29, 2006 7:42 pm

The air you breath in contains 21 % O2 78% N and 1% other gasses (mostly argon then CO2)
When you exhale the air still contains about 15% O2 and alot mot CO2 (im not sure if it 6% or not). Anyway that 15% O2 is waisted on normal open circuit or OC scuba gear.
With a closed circuit or CC rebreather you can have a tank full of 100% O2. As you breath this gas it flows from the tank to your lungs and then out to a scrubber. The scrubbers purpose is to remove the CO2. This is done by a chemical reaction with a substance in the scrubber. One such substance is soda lime. If I recall correctly the net effect of CO2 and soda lime is chalk. Obviously after the dive you change out the soda lime (chalk) for fresh stuff.
Once the exhaled gas has been thru the scrubber it comes out as pure O2 again to be "rebreathed". A little fresh O2 is added to the loop from the tank to compensate for the O2 you have breathed and as you decend more O2 is added to compensate for gas compression at depth.
As you can see you dont use nearly as much gas as OC scuba and there are only exhaust bubles when you ascend and the gas in the loop expands.
There are limitations though. When diving with pure O2 you are limited to 6meter depths due to high PPO or partial pressure of oxygen. This you should understand if you have done a nitrox class or if you had a good open water instructor.
You can also get rebreathers that have 2 tanks. 1 of pure O2 and the other of Nitrox, air or trimix. This second tank is called a {insert forgoten name here}. Its job is to supply the right mix for the dive and to flush out the loop in the even of water entering and also to add more gas for when you decend but the rebreather mainly adds O2 from the O2 tank to replace the gas you consume.
There is also a Semi Closed Circuit or SCC rebreather that uses more air than a CC rebreather and puts out more exhaust bubbles.
I think rebreathers have been around longer than scuba.

I am no rebreather expert and I am sure I have mad a few mistakes in the above but the basis of it should be correct.

edit: second tank is called dilutant and can also used as a bailout gas supply if the rebreather fails.
Last edited by Packhorse on Wed Nov 29, 2006 9:26 pm, edited 1 time in total.
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Postby Packhorse » Wed Nov 29, 2006 7:59 pm

Rebreathers are not just for underwater use either. Other uses include fire fighting, mining and of course outer space.

http://science.howstuffworks.com/question632.htm
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Postby Mermaid » Fri Dec 01, 2006 12:08 pm

Fantastic! That's a lot to take in but you've answered all my questions - apart form the ones below (sorry!) thank you.

Have you used one? What is it like? do you think all divers will be using them in the future?

I saw a program on them last night funnily enough and I can see how thay would be ideal for photographers and military divers!

Cheers, Anna :D
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Postby Packhorse » Fri Dec 01, 2006 1:34 pm

I have never used one. Yet. Plenty of experianced people have died using them, they are a lot more complicated than OC scuba and alot more expencieve. One day when they develop an idiot proff and cheap design then maybe everyone will use one.
I think the most dangerous aspect is the continuing mixing of the gases. Too much CO2 will kill you as will too much or to little O2.
Incidently I have seen plans for $3 rebreather on the net before.

http://www.geocities.com/chickenheadlab ... ather.html

And here is a really good artical about nitrox that includes O2 toxicity and explains about PPO or Partial Pressure of Oxygen if you do not already know.

http://www.gasdiving.co.uk/pages/misc/Nitrox.htm
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Postby silent solutions » Sat Feb 24, 2007 12:48 pm

most of the time oxygen is your friend on a rebreather to much is not a problem as it can be breathed down or diluted not enough is where the bad things happen as with a co2 hit.
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