Soda lime

[1] Medical-grade soda lime includes an indicating dye that changes color when it reaches its carbon dioxide absorption capacity.

To ensure proper functioning, a carbon dioxide scrubber (or soda lime canister) should not be used if the indicating dye is activated.

[2][3] However, in larger settings like recompression chambers or submarines, a fan is employed to ensure a continuous flow of gas through the scrubbing canister.

Notably, the use of indicating dye in United States Navy fleet applications ceased in 1996 due to concerns about potential chemical releases into the circuit.

[5] The reaction mechanism of carbon dioxide with soda lime can be decomposed in three elementary steps: This sequence of reactions explains the catalytic role played by sodium hydroxide in the system and why soda lime is faster in chemical reactivity than calcium hydroxide alone.

[8][9] The same catalytic effect by the alkali hydroxides (function of the Na2Oeq content of cement) also contributes to the carbonation of portlandite by atmospheric CO2 in concrete although the rate of propagation of the reaction front is there essentially limited by the carbon dioxide diffusion within the concrete matrix less porous.