<Li> Surface supplied diving distributes the task loading between the divers and the support team, who remain in the relative safety and comfort of the surface control position . Gas supplies are limited only by what is available at the control position, and the diver only needs to carry sufficient bailout capacity to reach the nearest place of safety, which may be a diving bell or lockout submersible . </Li> <Li> Saturation diving is a procedure used to reduce the high risk decompression a diver is exposed to during a long series of deep underwater exposures . By keeping the diver under high pressure for the whole job, and only decompressing at the end of several days to weeks of underwater work, a single decompression can be done at a slower rate without adding much overall time to the job . During the saturation period the diver lives in a pressurized environment at the surface, and is transported under pressure to the underwater work site in a closed diving bell . </Li> <P> Amongst technical divers, there are divers who participate in ultra-deep diving on SCUBA below 200 metres (660 ft). This practice requires high levels of training, experience, discipline, fitness and surface support . Only twelve persons are known to have ever dived below a depth of 240 metres (790 ft) on self - contained breathing apparatus recreationally . That is the same number as the number of people who walked on the moon . The Holy Grail of deep scuba diving was the 300 m (980 ft) mark, first achieved by John Bennett in 2001, and has only been achieved five times since . </P> <P> The difficulties in relation to ultra-deep diving are numerous . Although commercial and military divers often operate at those depths, or even deeper, they are surface supplied . All of the complexities of ultra-deep diving are magnified by the requirement of the diver to carry (or provide for) their own gas underwater . These leads to rapid descents and "bounce dives". Unsurprisingly, this has led to extremely high mortality rates amongst those who practise ultra deep diving . Notable ultra deep diving fatalities include Sheck Exley, John Bennett, Dave Shaw and Guy Garman . Mark Ellyatt, Don Shirley and Pascal Bernabé were involved in serious incidents and were fortunate to survive their dives . Despite the extremely high mortality rate, the Guinness Book of World Records continues to maintain a record for scuba diving (although in deference to the death rate it has stopped recording the record for deep diving on air). Amongst those who do survive significant health issues are reported . Mark Ellyatt is reported to have suffered permanent lung damage; Pascal Bernabé (who was injured on his dive when a light on his mask imploded) and Nuno Gomes reported short to medium term hearing loss . </P>

How deep can man dive in the ocean