Soda lime
Soda lime is a mixture of chemicals, often used in granular form in rebreathers to remove carbon dioxide from breathing gases to prevent carbon dioxide poisoning.The main components of soda lime are :
- Calcium Hydroxide - Ca(OH)2 (about 75%)
- Water - H2O (about 20%)
- Sodium Hydroxide - NaOH (about 3%)
- Potassium Hydroxide - KOH (about >0-1%
Soda lime is caustic and can cause burns to the eyes and skin. A "caustic cocktail" is a mixture of water and soda lime that happens when the "scrubber" floods.
In rebreather diving, the term "break through" describes the failure of the "scrubber" to continue removing cabon dioxide from the exhaled gas mix. Normally, it is the diver's responsibility to monitor the exposure time of the soda lime in the "scrubber" and replace it within the recommended time limit. Typically, the duration will be one to five hours of breathing depending on the granularity and composition of the soda lime and the design of the rebreather.
"Break through" occurs sooner on deep dives than on shallow dives. The reason for this is the proportion of carbon dioxide molecules passing over the soda lime granules is much lower at depth than the proportion of molecules of other component gases. This means the carbon dioxide molecules find it diffcult to come in contact with the soda lime granules because the granules are covered by the other gases. So, the carbon dioxide is not "scrubbed" but can be re-inhaled. There are two reasons for this:
- The metabolism, for a given rate of exertion, produces the same partial pressure of carbon dioxide irrespective of depth
- The partial pressures of the other gases in the [breathing gas]] increases with depth