Rebreathers:Carbon Dioxide and Soda Lime, what’s not to

love?

By Griffen Price

What is a Rebreather?A rebreather or “closed-circuit breathing

apparatus” is a device which removes the carbon dioxide from the air we exhale and “recycles” the unused oxygen back into our lungs (“Rebreather” 2).

Cellular Respiration and ATPBefore we get into how breathing in a closed

circuit works, we must first understand how breathing normally works.

We inhale air to supply oxygen to cellular respiration. This process is basically a chemical reaction between glucose, C6H12O6, and oxygen, O2, which produces ATP (adenosine triphosphate, the “energy currency” of cells), some water, and carbon dioxide (Nave 1).

Cellular Respiration (cont.)

Oxygen “Leftovers”Our body primarily rids itself of this CO2

byproduct through the lungs by way of exhaling (Graham 11).

When it does this, it also pushes out a whopping 80% of the oxygen initially breathed in before it has a chance to be absorbed into the body (Graham 12).

Usually, this expelled oxygen diffuses into the outside air; however, a rebreather captures and reuses it.

Unfortunately for us, this oxygen is also mixed up with nitrogen, carbon dioxide, and other gases, so we must use Chemistry to sift it out!

Holy Solenoids!The rebreathing process begins by carrying

the exhaled breath down an air hose and through an electric pressure-control valve called a solenoid.

Based on data from a computerized concentration-monitoring system, this solenoid mixes oxygen from an external tank with the air already in the system to keep oxygen supply at a steady level throughout the cycle (Borel 1).

CO2 Scrubbers and YouNext the mixture enters the scrubber: a small canister

packed with a granulated mixture known as soda lime. This is where the reactions happen.

Soda lime— a combination of calcium, potassium, and sodium hydroxides— reacts with the CO2 to form solid

carbonates as well as some water and heat (Graham 13):

Ca(OH)2 + CO2 CaCO3 + H20 + heat

2NaOH + CO2 Na2CO3 + H20 + heat

2KOH+ CO2 K2CO3 + H20 + heat

From here, the inert gases not involved in the reaction, namely oxygen and nitrogen, are free to move on through the scrubber and into more air tubes.

Chemical Composition of Soda Lime(These are the average percentages of the various compounds that compose soda lime.)

•Ca(OH)2: about 75%•H2O: about 20%•NaOH: about 3%•KOH: about 1%(Graham 13)

Calcium HydroxideWaterSodium HydroxidePotassium Hydroxide

The Counterlung and Diluent CylinderAfter exiting the scrubber, the oxygen and

nitrogen are drawn into a flexible bladder, the counterlung. Along with the diluent clylinder, this regulates pressure.

At this stage, a mechanical valve detects if there is enough pressure in the counterlung for the wearer to inhale again. If not, the diluent cylinder opens and releases more nitrox into the system, raising the pressure in the counterlung.

Once the pressure is sufficient, the conterlung opens and the air is inhaled through mouthpiece by a one-way valve (Borel 1).

All Together Now!•Here we can see the entire cycle of a rebreather mechanism and understand how it constantly recirculcates the oxygen and supports

And this matters Why?Rebreathers are an essential device in fiction: popular

heroes such as the Spy Kids, James Bond, and Batman have escaped many a danger using this hand-dandy underwater life support.

Rebreather systems are used in a variety of important fields (Mathworld 19):Workers in mine rescue and industry utilize the device in

oxygen-poor conditions or in environments with airborne toxins.

Hospitals employ it to control the breathing atmosphere of intensive-care patients without changing the ambient air.

Astronauts have relied on these systems for decades to keep them alive inside their space suits (Graham 13). Without rebreathers, we’d wouldn’t have landed on the Moon!

Works CitedBorel, Brooke. "How It Works: Recycled-Air Scuba System | Popular Science." Popular Science. Bonnier Corporation, n.d. Web. 24 Apr. 2013.< http://www.popsci.com/content/recycled-air-scuba-system  >

Graham, Tim. "Rebreathers" ChemMatters, Feb. 2008. Print.

MathWorld. "Diving Physics & The Chemistry Behind Rebreathers." Ouchmath. WordPress, 19 Jan. 2011. Web. 24 Apr. 2013.< http://ouchmath.wordpress.com/2011/01/19/diving-physics/  >

Nave, R. "Cellular Respiration." Cellular Respiration. Georgia State University, n.d. Web. 24 Apr. 2013.< http://hyperphysics.phy-astr.gsu.edu/hbase/biology/celres.html  >

"Rebreather." Chemistry Daily. Chemistry Daily, 1 Apr. 2007. Web. 27 Apr. 2013.< http://www.chemistrydaily.com/chemistry/Rebreather  >