2. 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).
3. Cellular Respiration and ATP
Before 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).
5. 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!
6. 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).
7. CO2 Scrubbers and You
Next 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.
8. 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
Hydroxide
Water
Sodium
Hydroxide
Potassium
Hydroxide
9. The Counterlung and Diluent Cylinder
After 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).
10. All Together
Now!
•Here we can see
the entire cycle of
a rebreather
mechanism and
understand how it
constantly
recirculcates the
oxygen and
supports
11. 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!
