TheClearance Divers Breathing Apparatus (CDBA) is a type ofrebreather made bySiebe Gorman inEngland.
The BritishRoyal Navy used it for many years.[1] It was for underwater work rather than for combat diving. The mainoxygencylinders are on the diver's back. The oxygen cylinders at the front of the diver are forbailout. In its basic mode it was an oxygen rebreather; but some of the cylinders could be replaced by diluent cylinders fornitrox mode (which the Navy called "mixture"), and then the set was sometimes called CDMBA.[clarification needed] 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 calledDSSCCD from "Diving Set, Self-Contained, Clearance Diver".
The CDBA was very popular with theclearance divers. It is comfortable since there is no cylinder on the middle of the back, no bulkybuoyancy compensator, and it requires very little weight.[2]
As the rebreather has a single "pendulum"breathing tube, the diver must breathe deeply to avoidcarbon dioxide build-up. Thecounterlung is eight litres.[2] 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.[2]
Instead of a weight belt there is a weight pouch at the back, full of lead ball weights 38 mm (1.5 in) in diameter. In an emergency, the diver could pull a line which opened the weight pouch to jettison these weights.[citation needed]
It is intended to be used with afullface mask with one breathing tube. At first (duringWorld War II and after) a mask with an oval or circular flat window (as seen in images atthis link) was used; later the mask with the newer type of rectangular window mostly flat but folded back at the sides was used.[citation needed]
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 circuitscuba.
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.[citation needed]
British "frogman's" sets used the same shape ofcounterlung 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 (nitrox orheliox) mode it was calledSCMBA. 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.[citation needed]
TheLOSE (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.[citation needed]
Other British frogmen's sets had no back cylinders and one or more big cylinders across the belly: one of these modes was theUBA (Underwater Breathing Apparatus).[citation needed]
For other uses of the letters "UBA" seeUBA.
