History of CO2 adsorbents for rebreathers in dive and other markets


	A little history Rebreathers were invented in the early 1700’s, and were first used in mine rescues. They remained primarily as land based devices until the late 1800’s when they were adapted for underwater use. The U.S. Navy has used SCUBA rebreathers since the 1930’s and all of the national militaries continue to use them for covert operations. Land based rebreathers are used in mine safety, fire fighting and medical applications. The recreational dive market is now seeing SCUBA rebreathers in greater numbers as the technology has become more user friendly and less expensive. Operation A rebreather in its simplest form is a closed circuit breathing device consisting of a breathing loop, gas supply, breathing bags and a CO₂ canister (see definitions). A key feature of a rebreather is that it extends the life of the gas supply allowing the user to carry a smaller, lighter tank. Air contains 21% oxygen, yet only 4 – 5% is metabolized on each breath. As the name implies, a rebreather allows you to re-circulate your expired breath by passing it through a carbon dioxide canister, which chemically removes most of the CO₂. Since usable oxygen remains, oxygen is only added as needed thereby extending the life of the tank. Anywhere that oxygen is used, especially in a self-contained breathing apparatus, a rebreather can provide a lighter weight, longer lasting supply of gas. There are many potential uses not discussed here and they are sure to start appearing as the technology becomes more refined.

	SCUBA rebreathers have several added advantages over conventional open circuit SCUBA, such as: few or no bubbles, warm and moist air in the breathing loop, longer bottom time, quiet operation and lower weight. Until recently, only the military and professional divers such as underwater photographers used SCUBA rebreathers. Due to advances in technology, rebreathers are now used in recreational diving as well. Almost every major hardware manufacturer has or is developing a rebreather for the sport market.

	Rebreathers are extensively used in hospital anesthesia systems, where they are used to scrub CO₂ from the closed circuit breathing loop that supplies gases to patients undergoing surgery. These systems allow very tight control of anesthesia gases, while the rebreather scrubs CO₂ from the loop. They are also being relied on in ambulatory situations, where oxygen is needed to treat patients under emergency conditions. One well-known medical application is in the dive market where DCS (decompression sickness) is treated with oxygen. The rebreather is contained in a suitcase which is carried on dive boats to extend the limited supply of oxygen that is typically available. The same type of units will eventually be used on ambulances and other emergency vehicles.

	All submarines use CO₂ scrubbing systems to maintain the quality of the air on the ship. Canister type canisters are used as backup or primary CO₂ canisters. These systems typically use Lithium Hydroxide as the adsorbent since it is more reactive.

	Fire fighters are starting to use rebreathers in fires where more than 30 minutes of air is needed. Existing air tanks rarely last longer than a half an hour, while rebreathers can last 1 or 2 hours without a substantial weight penalty. In high rise building fires or large structures the additional time could mean the difference between life and death. Rebreathers are also still used in mine safety and rescue as well as in industrial safety applications where people work in hazardous environments.