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

See also

• Lithium hydroxide