Soda lime

Soda lime is a mixture of chemicals, used in granular form in closed breathing environments, such as general anaesthesia, submarines, rebreathers and recompression chambers, to remove carbon dioxide from breathing gases to prevent CO2 retention and carbon dioxide poisoning.

It is made by slaking quicklime with concentrated caustic soda solution.

Chemical components
The main components of soda lime are
 * Calcium hydroxide, Ca(OH)2 (about 75%),
 * Water, H2O (about 20%),
 * Sodium hydroxide, NaOH (about 3%), and
 * Potassium hydroxide, KOH (about 1%).

Scrubber in a rebreather
Exhaled gas must be passed through a "carbon dioxide scrubber" where the carbon dioxide is absorbed before the gas is made available to be breathed again. In rebreathers the scrubber is a part of the breathing loop. In larger environments, such as recompression chambers, a fan is used to pass gas through the canister.

Chemical reaction

 * 1) CO2 + H2O → H2CO3
 * 2) H2CO3 + 2NaOH → Na2CO3 + 2H2O + Heat
 * 3) Na2CO3 + Ca(OH)2 → CaCO3 + 2NaOH
 * 4) Ca(OH)2 (heat) → CaO + H2O