<P> To dive safely, divers must control their rate of descent and ascent in the water and be able to maintain a constant depth in midwater . Ignoring other forces such as water currents and swimming, the diver's overall buoyancy determines whether they ascend or descend . Equipment such as diving weighting systems, diving suits (wet, dry or semi-dry suits are used depending on the water temperature) and buoyancy compensators can be used to adjust the overall buoyancy . When divers want to remain at constant depth, they try to achieve neutral buoyancy . This minimises the effort of swimming to maintain depth and therefore reduces gas consumption . </P> <P> The buoyancy force on the diver is the weight of the volume of the liquid that they and their equipment displace minus the weight of the diver and their equipment; if the result is positive, that force is upwards . The buoyancy of any object immersed in water is also affected by the density of the water . The density of fresh water is about 3% less than that of ocean water . Therefore, divers who are neutrally buoyant at one dive destination (e.g. a fresh water lake) will predictably be positively or negatively buoyant when using the same equipment at destinations with different water densities (e.g. a tropical coral reef). The removal ("ditching" or "shedding") of diver weighting systems can be used to reduce the diver's weight and cause a buoyant ascent in an emergency . </P> <P> Diving suits made of compressible materials decrease in volume as the diver descends, and expand again as the diver ascends, causing buoyancy changes . Diving in different environments also necessitates adjustments in the amount of weight carried to achieve neutral buoyancy . The diver can inject air into dry suits to counteract the compression effect and squeeze . Buoyancy compensators allow easy and fine adjustments in the diver's overall volume and therefore buoyancy . </P> <P> Neutral buoyancy in a diver is an unstable state . It is changed by small differences in ambient pressure caused by a change in depth, and the change has a positive feedback effect . A small descent will increase the pressure, which will compress the gas filled spaces and reduce the total volume of diver and equipment . This will further reduce the buoyancy, and unless counteracted, will result in sinking more rapidly . The equivalent effect applies to a small ascent, which will trigger an increased buoyancy and will result in accelerated ascent unless counteracted . The diver must continuously adjust buoyancy or depth in order to remain neutral . Fine control of buoyancy can be achieved by controlling the average lung volume in open circuit scuba, but this feature is not available to the closed circuit rebreather diver, as exhaled gas remains in the breathing loop . This is a skill which improves with practice until it becomes second nature . </P>

What is the importance of deep sea diving