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Occasionally an octopus is found in a small recess in a reef.


Their tentacles armed with suction cups are mainly used to help them attach their prey.


In contrast to scuba diving apparatus, the closed circuit oxygen rebreather provides a less wasteful means of self-contained movement underwater. This particular set was produced by the Divers’ Equipment Supply Company, based in Milwaukee, Wisconsin, USA during the 1940s.

In its simplest form a rebreather consists of an oxygen supply with an adjustable flow, a carbon dioxide absorbing canister containing an alkali such as soda lime and a reservoir or counter lung.

The diver breathes back and forth to the counter lung, each breath passing through the absorbent, which removes the carbon dioxide. Fresh oxygen replenishes the lost volume. The system needs pure oxygen, and is thus restricted to 10 metres. However little gas is wasted and a long duration may be achieved.

This type of apparatus was manufactured in Germany by Draeger, in Britain by Siebe Gorman, in Italy by Cressi-sub and by others in the USA during the war years of the 1940s.



Apart from this military use, sports and scientific divers, such as Hans Hass, took up the apparatus. In addition, early British cave divers used the equipment at sites such as Wookey Hole. However, there were problems.

In the trade such equipment came to be known, rather unaffectionately, as ‘One breath from death’. The two advantages of the closed circuit rebreather system are that no bubbles are produced and a greater underwater endurance may be achieved. However, the disadvantages can be severe:-

Menschen unter Haien (Men Amongst Sharks) HANS HASS, 1942

If a diver should proceed deeper than the current recommended limit of 6m, then a pressure will soon be reached at which the oxygen, vital for supporting biological life, becomes an absolute poison. Once the limit has been exceeded a fit and subsequent drowning are the likely consequences. Hans Hass demonstrates this problem, from which he was fortunately able to survive.


There is also the danger of producing a caustic soda mouthwash once saltwater mixed with the soda lime. This substance is generally preferred for cleaning the bath, rather than teeth and lungs!

Finally there is a need to purge unwanted nitrogen from the system. Air contains 20% oxygen and 80% nitrogen, all of which must be replaced in the breathing bag and lungs by oxygen for the apparatus to work safely. The system is purged of nitrogen by taking the contents of the breathing bag in through the mouth and out through the nose, three times. Failure to carry out this operation properly can result in anoxia and death.



In order to extend the depth capability of this type of equipment a semi-closed circuit mixed gas rebreather was developed. Here we see a postwar military clearance breathing apparatus, the C.D.B.A. The gas used is an elevated percentage of oxygen in air - nitrox - with mixes between: 60% oxygen, 40% nitrogen, for up to 20m depth, and 32½% oxygen, 67½% nitrogen, for depths of up to 50m.

The mixture is chosen for achieving a target depth, whilst reducing the nitrogen in the body and thereby decompression time.

This mechanical apparatus relies on a ‘flow orifice’ to regulate the rate of delivery of the mixed gas. The excess gas is dispersed from the breathing bag via a sort of spring loaded pepper pot. This disperses the bubbles into a fine mist, thus retaining some covert military advantage.


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