There is more and more talk of rebreathers, stated as being the future of diving. However, not many people have tried them. So what is all the fuss about?
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It is reliable, more or less foolproof, and its simple construction is very robust. These are good properties to have when one’s underwater breathing depends on them. However, as we will see, there are also a number of disadvantages. And it is these that make re-breathers an interesting alternative system.
When diving with a regulator, it is said that one is diving with an open circuit, because the exhaled air passes straight out into the surrounding water, and is thereby lost. As only about a quarter of the available oxygen has been taken up by the body, and the rest expelled, it is a rather ineffective utilisation of a scanty resource. (See table next page.)
In addition, as the amount of air used increases proportionally with depth, open systems become more and more inefficient, and there are therefore major limitations to how long a diver can remain underwater. It seems obvious, then, to try to re-use the air that has been exhaled, by using a closed system.
Closed circuit systems
Closed circuit systems are a far from new idea. It was Giovanni Borelli in the 1700’s who first thought of re-using the exhaled air. His idea was to recirculate the air through a copper tube which was cooled by the sea water, and thereby “cleaned” the air before re-use. Luckily, it was never made. The mining industry and its problems with gas in the mine shafts also stimulated the relevant technical developments during the 1700’s.
Henry Fleuss, an English naval officer from Germany, worked out the principles for a re-breathing apparatus, and produced a prototype at the end of the 1870’s. He stayed down in a water tank for nearly an hour, and later went down to 5 meters in a lake using his system. Fleuss was the first “diver” in history with a re-breathing apparatus. At the beginning of the 1900’s the military were quick to take up this idea.
Oxygen-rebreathing equipment consisted of an oxygen tank together with a bag of potassium hydroxide and a breathing loop, and was used to rescue submarine crews and attack divers (there were no revealing bubbles on the surface). The German manufacturer Dräger released several models for military use in connection with World Wars I and II.
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