The Clearance Divers Breathing Apparatus (CDBA) is a type of

rebreather A rebreather is a breathing apparatus that absorbs the carbon dioxide of a user's exhaled breath to permit the rebreathing (recycling) of the substantial unused oxygen content, and unused inert content when present, of each breath. Oxygen is a ...

made by

Siebe Gorman Siebe Gorman & Company Ltd was a British company that developed diving equipment and breathing equipment and worked on commercial diving and marine salvage projects. The company advertised itself as 'Submarine Engineers'. It was founded by Augu ...

England England is a Countries of the United Kingdom, country that is part of the United Kingdom. It is located on the island of Great Britain, of which it covers about 62%, and List of islands of England, more than 100 smaller adjacent islands. It ...

. The British

Royal Navy The Royal Navy (RN) is the naval warfare force of the United Kingdom. It is a component of His Majesty's Naval Service, and its officers hold their commissions from the King of the United Kingdom, King. Although warships were used by Kingdom ...

used it for many years. It was for underwater work rather than for combat diving. The main

oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...

cylinders A cylinder () has traditionally been a three-dimensional solid, one of the most basic of curvilinear geometric shapes. In elementary geometry, it is considered a prism with a circle as its base. A cylinder may also be defined as an infinite ...

are on the diver's back. The oxygen cylinders at the front of the diver are for

bailout A bailout is the provision of financial help to a corporation or country which otherwise would be on the brink of bankruptcy. A bailout differs from the term ''bail-in'' (coined in 2010) under which the bondholders or depositors of global syst ...

. In its basic mode it was an oxygen rebreather; but some of the cylinders could be replaced by diluent cylinders for

nitrox Nitrox refers to any gas mixture composed (excepting trace gases) of nitrogen and oxygen. It is usually used for mixtures that contain less than 78% nitrogen by volume. In the usual application, underwater diving, nitrox is normally distinguished ...

mode (which the Navy called "mixture"), and then the set was sometimes called CDMBA. The Royal Navy was using nitrox from 1944, but did not reveal its nitrox techniques, and in the 1960s and afterwards civilian divers had to retread the same ground and develop nitrox diving independently. In later years it was called DSSCCD from "Diving Set, Self-Contained, Clearance Diver".

Design

The CDBA was very popular with the

clearance divers A clearance diver was originally a specialist naval diver who used explosives underwater to remove obstructions to make harbours and shipping channels safe to navigate, but the term "clearance diver" was later used to include other naval under ...

. It is comfortable since there is no cylinder on the middle of the back, no bulky buoyancy compensator, and it requires very little weight. As the rebreather has a single "pendulum" breathing tube, the diver must breathe deeply to avoid

carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...

build-up. The

counterlung A rebreather is a breathing apparatus that absorbs the carbon dioxide of a user's exhaled breath to permit the rebreathing (recycling) of the substantial unused oxygen content, and unused inert content when present, of each breath. Oxygen is ad ...

is eight litres. As with all rebreathers, the diver should breathe continuously to keep the gas flowing over the absorbent. Dives on the unit are limited to 90 minutes. Instead of a weight belt there is a weight pouch at the back, full of lead ball weights in diameter. In an emergency, the diver could pull a line which opened the weight pouch to jettison these weights. It is intended to be used with a

fullface mask A full-face diving mask is a type of diving mask that seals the whole of the diver's face from the water and contains a mouthpiece, demand valve or constant flow gas supply that provides the diver with breathing gas. The full face mask ha ...

with one breathing tube. At first (during

World War II World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...

and after) a mask with an oval or circular flat window (as seen in images a
this link
was used; later the mask with the newer type of rectangular window mostly flat but folded back at the sides was used.

Modes of setting up the CDBA

The front cylinders were intended as a bailout; the main cylinders are on the back. For a short dive the set could be used without the back cylinders, using only the front cylinders; this made the set very light and compact and suitable for getting through small holes. Even with the back cylinders the diver is much more compact and streamlined and agile than most recreational open circuit

scuba Scuba, originally SCUBA, often expanded to scuba set, is any self contained underwater breathing apparatus, a source of breathing gas used for underwater diving which is carried by the diver. Scuba may also refer to: * Scuba diving, swimming unde ...

. The front and the back of the harness can unclip from each other at the shoulders. There is no automatic gas control: so safe use of the set relied entirely on training.

Other similar rebreathers

2 frogmen with SCBA 1950s-type rebreathers

British British may refer to: Peoples, culture, and language * British people, nationals or natives of the United Kingdom, British Overseas Territories and Crown Dependencies. * British national identity, the characteristics of British people and culture ...

"frogman's" sets used the same shape of

as the CDBA but different cylinders. One type was the "Swimmer Canoeists Breathing Apparatus" (SCBA), which had oxygen cylinders on the back, vertically for better streamlining in swimming, the oxygen connections thinner, and no cylinders on the front, leaving the diver's lower front uncluttered for climbing in and out of small boats. The SCBA gave 90 minutes dive duration with no reserve. In mixture (

heliox Heliox is a breathing gas mixture of helium (He) and oxygen (O2). It is used as a medical treatment for patients with difficulty breathing because this mixture generates less resistance than atmospheric air when passing through the airways of ...

) mode it was called SCMBA. An old photograph seems to show the cylinders (and perhaps also the weights) in a tied or laced canvas casing rather than held on with metal clamps, and a rectangular fullface mask as with the CDBA. There is a British armed forces manual about the SCBA, dated 1984 as if the SCBA was still in use then, showing separate eyes-and-nose mask and strapped-in mouthpiece and no canvas pouch, and separate sport-type weight belt with buckle-shaped weights all at the back. The design of the Swimmer Canoeists Breathing Apparatus likely changed down the years. The LOSE (Lightweight Oxygen Swimmers Equipment), a diving rebreather formerly made by Siebe Gorman, was similar to a Swimmer Canoeist's Breathing Apparatus including the cylinder backpack. Other British frogmen's sets had no back cylinders and one or more big cylinders across the belly: one of these modes was the UBA (Underwater Breathing Apparatus).

Other meanings of those initials

*The letters "SCBA" had two other meanings connected to breathing sets: **Submerged Chamber Breathing Apparatus (formerly used to aerate submerged air-chambers). **

Self Contained Breathing Apparatus A self-contained breathing apparatus (SCBA) is a respirator worn to provide an autonomous supply of breathable gas in an atmosphere that is immediately dangerous to life or health from a gas cylinder. They are typically used in firefighting a ...

(its modern meaning, it means industrial breathing sets (usually open-circuit) for use on land) For other uses of the letters "UBA" see

UBA Uba or UBA (and diacritic variations) may refer to: Agriculture * Uba, a cultivar of '' Saccharum sinense'' Place names * Ubá, small tropical city in the state of Minas Gerais, Brazil * Uba, Nigeria, part of Askira/Uba Local Government Area in B ...

References

External links