Re-breathers made simple

Guten tag to my non existant german readers, and konichiwa to the rest of you.

Lets face it, I’m envious of those techies on the quayside in there cool gear however what i find that i yearn for the most is a bad ass re-breather. Not only does it add to your street cred when you bust out one of those bad boys but it’s actually and incredible clever and elegant piece of kit which has a fair few benefits to my faithful Apeks regulator.

Let us begin.

In conventional scuba gear, as you breathe in air is taken from the tank on you back and delivered to you through your mouthpiece. Then you breathe out the waste air and it’s expelled through the regulator forming pretty bubbles in the surrounding water. Simples.

A Closed circuit re-breather (CCR) allows you to breathe the same air again and again, without expelling any gases in the surrounding environment. However, in order for this to happen some clever magic has to go on in a funky hard-case which you carry on your back instead on a tank.

1) Remove exhaled carbon dioxide: To achieve this, exhaled gas passes through a cannister of Soda lime which contains several chemicals, the most important being Sodium hydroxide and calcium hydroxide. What goes in in this cannister is a simple neutralisation reaction. Remember back to chemistry class!

Acid + Alkali = Salt + water

so

Carbon Dioxide + Soda Lime = Salt + water

(for you chemistry nerds like me, I will post a tasty strong base catalysed, water facilitated reaction at the end!)

Sweet! Calcium carbonate forms as a solid but what about that pesky water? It’s actually quite handy as it helps to fight dehydration from breathing dry air for long periods.

2) Replace oxygen you have used: Small tanks carrying normally close to the hard-case inject oxygen (or mixed gases, normally Nitrox or Heliox) inhaled by you back in to the  loop.

3) Control oxygen concentration in the breathing loop: too much or too little oxygen is bad, mkay. Therefore a clever little gadget called a ‘solid state oxygen sensor’ monitors the partial pressure of oxygen and sends results to a microprocessor in the gas delivery system. Cool huh?

All pretty common sense if you take the time to sit down and struggle with it for a while. This is all very good and clever but how does it benefit us, the diving community?

As far as I can see, there are 4 main bonuses to this system:

  • Improved gas efficiency – normal SCUBA systems waste a lot of oxygen considering our lungs aren’t great at absorbing oxygen, therefore exhale a lot of it which is then wasted! Rebreathers only replace absorbed oxygen so don’t waste gas.
  • Lighter – normal air contains about 78% oxygen therefore the majority of weight in a normal cylinder is useless nitrogen. Rebreathers don’t have to carry nitrogen so for the same amount of oxygen, can be lighter.
  • Less Decompression – Because the nitrogen in the system, which is involved in “the bends”, is kept to a minimum, decompression is less complicated and divers can stay down longer than with conventional scuba.
  • Stealth: Rebreathers produce few or no bubbles, so they don’t disturb marine life or reveal the diver’s presence.

There we have it folks, the basics (and I do mean the basics). After trolling for hours through swathes of really complicated PDF files, forums and website i think I’ve separated the wheat from the chaff and given you a little bit of ammunition to impress you friends or deflate the ego of a tec diver and their debonair hardhats.

More rebreather stuff will follow this considered I’m obsessed with the thing at the moment. Hope you enjoyed this relatively theory heavy post!

Rob

WARNING: CHEMISTRY BANTER FOLLOWS

Welcome friends to the nerd zone. Here as promised is that cheeky reaction in full. Enjoy.

The overall reaction is:

CO2 + Ca(OH)2 → CaCO3 + H2O + heat (in the presence of water)

The reaction can be considered as a strong base catalysed, water facilitated reaction.

1) CO2 + H2O → CO2 (aq) (CO2 dissolves in water – slow and rate determining)

2) CO2 (aq) + NaOH → NaHCO3 (bicarbonate formation at high pH)

3) NaHCO3 + Ca(OH)2 → CaCO3 + H2O + NaOH (NaOH recycled to step 2) – hence a catalyst)
Each mole of CO2 (44g) reacted produces one mole of water (18g)

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4 responses to “Re-breathers made simple

    • This is a good question!

      However my main concern would be this. Say you went abroad and you wanted to do some diving that involved using a Rebreather and presented a PADI certification card, seeing as its a world recognised brand there would be no problems hiring out equipment.

      However with RAID I’m not sure, as relatively new organisation compared to PADI, how widespread they are at the moment. For example i know that they are looking for representatives to spread the brand in the USA.

      Training wise it looks excellent with comprehensive steps to train. All that being said the base cost for the RAID sessions is £170 plus ‘pool sessions’ which i cant seem to find how many/ how long they are. Not necessarily a ‘hidden’ cost by any means but definitely something to consider.

      Also have you done any diving before? Since the PADI prerequisites you to be a Enriched Air diver as well as an Advanced open water diver (sneaky).

      Hope this helps!

      Any other questions please feel free to ask 🙂

      Rob

      PADI on the other

      • Hi Rob, Thanks for that, yep i’m actually a divemaster and already tried out a rebreather before so i can transfer straight to level 2 advanced rebreather. The only reason i was thinking of doing RAID is that my friend is an instructor and will do it for me at cost price, but might push him to complete his transfer to PADI so then i can get PADI qualified if their are worries about the internationality of RAID, all my other qualifications are PADI so i guess it makes sense for me to continue with PADI.

        Thanks again for the advice =)

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