Breathing sets operating on the above principles are not only used underwater but in other situations where the atmosphere is dangerous (little oxygen, poisonous etc).
Firefighting
Other jobs out of water, e.g. welding in a confined space
Mining, especially mine rescue
Operations in enclosed or poorly ventilated areas, e.g. large fluid or gas containers.
These breathing sets are nowadays called SCBA (Self Contained Breathing Apparatus) (The initials SCBA have had other meanings). The first open-circuit industrial breathing sets were designed by modifying the design of the Cousteau aqualung.
Industrial rebreathers have been used since soon after 1900.
Rebreather technology is also used in space suits.
History
Todays scuba sets are mostly similar to the ideas suggested by Alexander Lodygin many years before the term appeared.
A predecessor to scuba gear, the Momson lung, was used as emergency escape gear by WWII submariners.
Jacques-Yves Cousteau and Emile Gagnan invented the first commercially successful open circuit type of SCUBA diving equipment, the Aqua-Lung (often spelled "aqualung") in 1943. Among the things that prompted Cousteau to develop efficient air-breathing diving free-swimming diving gear, were two oxygen toxicity accidents that he had with rebreathers. The Cousteau Gagnan patent was licensed to Siebe Gorman of England. Siebe Gorman was allowed to sell in Commonwealth countries but had difficulty in meeting the demand and the US patent prevented others from making the product. Ted Eldred of Melbourne, Australia met this demand by developing the single hose regulator used today. Ted sold his first Porpoise model CA single hose scuba in early in 1952.
Another SCUBA pioneer was John Haven "Jack" Emerson, who also developed the iron lung and other breathing apparatus.
Before 1971 all breathing sets including scuba came with a plain harness of straps with buckles like on a rucksack or spray-tank-pack. The buckles were usually quick-release. Many did not have a backpack plate, but the cylinders were held directly against the diver's back. Sport scuba usually had quick-release fastenings instead of ordinary buckles. The harnesses of many diving rebreathers made by Siebe Gorman included a large back-sheet of strong reinforced rubber.
In the beginning scuba divers dived without any buoyancy aid. In emergency they had to jettison their weights. In the 1960s adjustable buoyancy life jackets for aqualung-type scuba became available; one early make was Fenzy. The ABLJ is used for two purposes, one to adjust the buoyancy of the diver to compensate for loss of buoyancy (chiefly due to compression of neoprene wetsuit) and more importantly as a lifejacket that can be rapidly inflated even at depth. It was put on before putting on the cylinder harness. The first were inflated with a small carbon dioxide cylinder, later with a small air cylinder. An extra feed from the first stage regulator lets the life jacket be controlled as a buoyancy aid.
Accessories
In modern scuba sets, a buoyancy compensator (BC) or buoyancy control device (BCD), such as a back-mounted wing or stabilizer jacket (otherwise known as a 'stab jacket'), is built into the scuba set harness. Although strictly speaking this is not a part of the breathing apparatus, it is usually connected to the diver's air supply, in order to provide easy inflation of the device. This can usually also be done manually via a mouthpiece, in order to save tank air while on the surface. The bladders inside the BCD inflate with air from the ‘direct feed’ to increase the volume of the SCUBA equipment and cause the diver to float. Another button deflates the BCD and decreases the volume of the equipment and causes the diver to sink. Certain BCD's allow for integrated weight, meaning that the BCD has special pockets for the weights that can be dumped easily in case of an emergency. The aim of using the BCD, whilst underwater, is to keep the diver neutrally buoyant, i.e. neither floating up or sinking. The BCD is used to compensate for the compression of a wet suit, and to compensate for the decrease of the diver's mass as the air from the cylinder is breathed away.
Diving weighting systems, ranging from 2 to 15 kilograms, increase density of the scuba diver to compensate for the buoyancy of diving equipment, allowing the diver to fully submerge underwater with ease by obtaining neutral or slightly negative buoyancy. While weighting systems originally consisted of solid lead blocks attached to a belt around the diver's waist, some modern diving weighting systems are now incorporated into the BCD. These systems use small nylon bags of lead shot pellets which are distributed throughout the BCD, allowing a diver to gain a better overall weight distribution leading to a more horizontal position in the water. There are cases of lead weights being threaded on the straps holding the cylinder into the BCD.
Many modern rebreathers use advanced electronics to monitor and regulate the composition of the breathing gas.
Some scuba sets incorporate attached extra stage cylinders, as bailout in case the main breathing gas supply is used up or malfunctions, or containing another gas mixture. If these extra cylinders are small, they are sometimes called "pony cylinders". They often have their own demand regulators and mouthpieces, and if so, they are technically distinct extra scuba sets.
The diver may carry two or more sets of breathing equipment to provide redundant alternative gas systems in the event that the other fails or is exhausted. Modern recreational rigs most often have two regulators connected to a single tank, in case the primary regulator fails or another diver runs out of air. Some divers instead connect their backup regulator to a smaller "pony cylinder" for extra safety, and there are also emergency systems which mount a simple regulator directly to the top of a small cylinder. Rebreather divers often carry a side-slung open-circuit "bail out" to be used in the event the rebreather fails.
In technical diving, the diver may carry different equipment for different phases of the dive; some breathing gas mixes may only be used at depth, such as trimix and others, such as pure oxygen, which only may be used during decompression stops in shallow water. The heaviest cylinders are generally carried on the back supported from a backplate while others are side slung from strong points on the backplate.
When the diver carries many diving cylinders, especially those made of steel, lack of buoyancy becomes a problem. High capacity buoyancy compensators are used to allow the diver to control his or her depth.
An excess of tubes and connections passing through the water tend to decrease diving performance by causing hydrodynamic drag in swimming.
Some diver training organizations and groups of divers teach techniques, such as DIR diving for configuring diving equipment.
] Notable early manufacturers
Normalair is a firm that is now part of the Honeywell Corporation based in Yeovil (UK). They made an early make of single-hose aqualung that had a fullface mask as standard. Normalair provided the Deep-Dive 500 rebreather sets used by James Bond 007 in the 1981 film For Your Eyes Only.
Captain Trevor Hampton in the 1950s or 1960s designed an early single-hose aqualung with a fullface mask with a circular window which was a very big and thus very sensitive demand regulator diaphragm. But when he patented it, the Navy requisitioned the patent, and by the time the Navy found no use in the patent and released it, the market had moved on and he got no use from the patent.
The first commercially successful single hose scuba inventor was Ted Eldred of Melbourne, Australia (Porpoise 1952), although many people were working on it at the same time.
The second company to make single hose scuba was also in Melbourne. It was made by Jim Ager who owned Air Dive Pty.Ltd. His regulator was the Sea Bee (1955). Jim still makes scuba regulators and is the longest continuous maker of single hose scuba in the world.
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