History of decompression research and development gets too high when compared to the ambient pressure. These bubbles, and products of injury caused by the bubbles, can cause damage to tissues known as "decompression sickness" or "the bends". The immediate goal of controlled decompression is to avoid development of symptoms of bubble formation in the tissues of the diver, and the long-term goal is to also avoid complications due to sub-clinical decompression injury. The symptoms of decompression sickness are known to be caused by damage resulting from the formation and growth of bubbles of inert gas within the tissues and by blockage of arterial blood supply to
Scuba set assembled as an integrated part of the set, but is not technically part of the breathing apparatus. The cylinder is usually worn on the back. "Twin sets" with two low capacity back-mounted cylinders connected by a high pressure manifold were more common in the 1960s than now for recreational diving, although larger capacity twin cylinders ("doubles") are commonly used by technical divers for increased dive duration and redundancy. At one time a firm called Submarine Products sold a sport air scuba set with three manifolded back-mounted cylinders. Cave and wreck penetration divers sometimes carry cylinders attached at their sides instead,