Deep diving

The meaning of the term "deep diving" is a form of technical diving. It is defined by the level of the diver's diver training, diving equipment, breathing gas, and surface support:
in recreational diving, 30 metres / 100 feet may be a 'deep dive'
in technical diving, 60 metres / 200 feet may be a 'deep dive'
in surface supplied diving, 100 metres / 330 feet may be a 'deep dive'

This definition essentially relates to recreational diving. Deep diving may have quite a different meaning in the commercial diving field. For instance the early experiments carried out by Comex S.A. (Compagnie maritime d'expertises) using hydrox and also nitrogen trimix attained far greater depths than any recreational technical diving. One example being the Comex Janus IV open-sea dive to 500 metres, in 1977. The open-sea diving depth record was achieved in 1988 by a team of Comex divers who performed pipe line connection exercises at a depth of 534 metres in the Mediterranean Sea as part of the Hydra 8 programme. These divers needed to breathe special gas mixtures because they were exposed to very high ambient pressure (more than 50 times atmospheric pressure). An atmospheric diving suit allows very deep dives of up to 700 metres. These suits are capable of withstanding the pressure at great depth permitting the diver to remain at normal atmospheric pressure. This eliminates the problems associated with breathing high pressure gases.


( class'wikitable' style'margin: 1em auto 1em auto'
+ "Deep Diving"
! width'150'DepthAll depths specified for sea water. Fractionally deeper depths may apply in relation to freshwater due to its lower density width'385'Comments
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align'center'40 feet/12 meters Recreational diving limit for divers aged under 12 years old and beginner divers.
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align'center'60 feet/18 meters Recreational diving limit for divers with Open Water certification but without greater training and experience.
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align'center'100 feet/30 meters Recommended recreational diving limit for divers. Average depth at which nitrogen narcosis symptoms begin to appear in adults.
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align'center'130 feet/40 meters Absolute recreational diving limit for divers specified by Recreational Scuba Training Council (RSTC).
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align'center'180 feet/55 meters Technical diving limit for 'extended range' dives breathing air to a maximum partial pressureppoxygenO2 of 1.4 Atmosphere (unit)ATA.
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align'center'218 feet/65 meters Depth at which compressed air results in an unacceptable risk of oxygen toxicityOxygen toxicity depends upon a combination of partial pressure and time of exposure, individual physiology, and other factors not fully understood. National Oceanic and Atmospheric AdministrationNOAA recommends that divers do not expose themselves to breathing oxygen at greater than 1.6 bar partial pressureppoxygenO2, which occurs at 218 feet breathing air.
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align'center'330 feet/100 meters Technical diving training limit for divers breathing Trimix (breathing gas)trimix. Recommended technical diving limit.
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align'center'509 feet/155 meters Record for scuba dive on compressed air.Set by Dr Dan Marion on March 18, 1994. The record is not officially recognised anywhere, and it should be noted that Dr Marion's second dive computer only registered a depth of 490 feet. See generally 'Deep Diving' by Bret Gilliam, ISBN 0-922769-31-1, at pages 35 and following.
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align'center'660 feet/200 meters Absolute limit for surface light penetrationAssuming crystal clear water; surface light may disappear completely at much shallower depths in murky conditions.
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align'center'1,083 feet/330 meters World record for deepest dive on SCUBA 1,083 feet was the depth reportedly achieved by Pascal Bernabé in 2005. However, the Guinness World Records still recognises the 1,044 feet dive by Nuno Gomes (diver)Nuno Gomes earlier in the same year as the current official world record.
)

Particular problems associated with deep dives

Deep diving obviously has more consequences and dangers than basic open water diving. Nitrogen narcosis, or the “narks” or “rapture of the deep”, starts with feelings of euphoria and over-confidence but then lead to numbness and memory impairment similar to alcohol intoxication. Decompression sickness, or the “bends”, is when the gas bubbles of nitrogen get caught in the joints on an ascent. Yet, the effects tend to be delayed until reaching the surface. Bone degeneration (dysbaric osteonecrosis) is caused by the bubbles forming inside the bones; most commonly the upper arm and the thighs. Air embolism causes Unconsciousnessloss of consciousness and speech and visual problems. This tends to be life threatening, but sometimes the symptoms resolve before the recompression chamber are needed. All these are the harmful, and possibly worse, effects of deep diving. These physical and physiological stresses require good Physical fitnessphysical conditioning.

High breathing gas consumption. Gas consumption is proportional to pressure - so at 50 metres / 165 feet (6 bar) a diver breathes 6 times as much as on the surface (1 bar). Heavy physical exertion causes even more gas to be breathed.
Increased nitrogen narcosis. This causes stress and inefficient thinking in the diver. When breathing breathing gasair many divers find 40 metres / 130 feet a safe maximum depth.
The need to do decompression stops increases with depth. A diver at 6 metres may be able to dive for many hours without needing to do decompression stops. At depths greater than 40 metres / 130 feet, a diver may have only a few minutes at the deepest part of the dive before decompression stops are needed. In the event of an emergency the diver cannot make an immediate ascent to the surface without risking decompression sickness. The diver needs a disciplined approach to planning and conducting dives and needs to carry extra gas for the decompression stops to reduce the risk of being unable to complete the stops.
Drifting. If long decompression stops are carried out in a tidestidal current, the divers may drift away from their boat cover or a safe exit point on the shore.
Increased breathing effort. Gas becomes Densitydenser and the effort required to breathe increases with depth (work of breathing).
Increasing risk of hypercapnia, an excess of carbon dioxide in the blood.
Oxygen toxicity.
High pressure nervous syndrome.

Dealing with depth
Divers carry larger volumes of breathing gas to compensate for the increased gas consumption and decompression stops.
Rebreathers manage gas much more efficiently than open circuit scuba, but are inherently more complex than open circuit scuba.
Use of helium-based breathing gases such as trimix (breathing gas)trimix reduces nitrogen narcosis and stays below the limits of oxygen toxicity.
A diving shot, a decompression trapeze or a decompression buoy can help divers return to their surface safety cover at the end of a dive.

Ultra-deep diving

( class'wikitable' style'float:right;'
+ "Verified SCUBA dives below 800 feet"
! Name Location Depth Year
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Nuno Gomes (diver)Nuno Gomes Red SeaRed SeaSouth AfricaSouth Africa align'right' align'center'2005200419961994
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Pascal Bernabé MediterraneanMediterranean align'right' 20052005
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David Shaw (diver)David ShawSubsequently died during diving accidents. South Africa align'right' 2004
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Gilberto M de Oliveira Brazil align'right' 2002
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John Bennett (diver)John Bennett PhilippinesPhilippines align'right' 20012001
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Jim Bowden (diver)Jim Bowden MexicoMexico align'right' align'center'19941993
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Sheck Exley South AfricaMexico align'right' 19931989
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Don Shirley (diver)Don Shirley South Africa align'right' 2005
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Mark Ellyatt Andaman SeaThailand align'right' 20032003
)

Amongst technical divingtechnical divers, there are certain elite divers who participate in ultra-deep diving on SCUBA (using rebreatherclosed circuit rebreathers and heliox) below . Ultra-deep diving requires extraordinarily high levels of training, experience, fitness and surface support. Only eight (or possibly nine) persons are known to have ever dived below a depth of on self contained breathing apparatus recreationally.Statistics exclude military divers (classified), and commercial divers (although commercial diving to that depth is unknown on SCUBA). In 1989 the US Navy experimental diving unit published a paper entitled 'EX19 (a type of experimental rebreather) Performance Testing at 850 and 450 feet sea waterFSW' which included a section on results from tests on the use of rebreathers at 850 feet. In 2007 Erdogan Bayburt, a former Turkish Navy diver, dived to a depth of off the coast of Cyprus, but that dive has not been independently verified. He used a closed-circuit rebreather. His dive was aborted due to equipment failure. It was a Turkish Navy experimental dive. That is fewer than the List_of_Apollo_astronautsApollo_astronauts_who_walked_on_the_Moonnumber of people who have walked on the surface of the moon. The Holy Grail of deep SCUBA diving was the mark, first achieved by John Bennett in 2001, and has only been achieved five times since. Dives of this nature have been impossible to verify - proof being as tangible as faith more often as not. Since the recent introduction of depth gauges capable of reading to 330m it is unlikely that such records will be attempted in the future.

In 2003 Mark Ellyatt dived to a depth of 260m and 313m, the details of the dives can be found at www.inspired-training.com. In 2004 2 Italian divers reached 316m and 320m both divers succumbing to devastating decompression sickness.

All of the foregoing dives were conducted on open circuit SCUBA equipment, except for David_Shaw_(diver)David Shaw and Don Shirley (diver)Don Shirley, who both used a closed-circuit rebreather.

Ultra deep air

Whilst extreme deep diving on air is extremely dangerous, before the popularity of Trimix attempts were made to set world record depths using conventional air. This created an extreme risk of both narcosis and oxygen toxicity in the divers and, perhaps unsurprisingly, contributed to an astonishgly high fatality rate amongst those attempting records. In his book, 'Deep Diving', Bret Gilliam chronicles the various fatal attempts to set records as well as the smaller number of successes. From the comparitively few who survived extremely deep air dives:
1947 Frederic Dumas, a colleague of Jacques Cousteau, dived to on air
1959 Ennie Falco reported having reached a depth of on air, but had no means to record it
1965 Tom Mount and Frank Martz dive to a depth of on air
1967 Hal Watts and AJ Muns dive to a depth of on air
1968 Neil Watson and John Gruener dived to on air in the Bahamas. Watson reported that he had no recollection at all of what transpired at the bottom of the descent due to narcosis.
1990 Bret Gilliam dives to a depth of on air. Unsually, Gilliam remains largely functional at depth and is able to complete basic maths problems and answer simple questions written on a slate by his crew beforehand.
1993 Bret Gilliam extends his own world record to , again reporting no ill effects from narcosis or oxygen toxicity.
1994 Dan Manion sets current record for a deep dive on air at . Manion reports he was almost completely incapacitated by narcosis and has no recollection of time at depth.
In deference to the high death rate, the Guinness World Records ceased to publish records on deep air dives.

See also
Decompression sickness
Breathing gas
Free-diving, diving without breathing
Heliox
Hydreliox
High pressure nervous syndrome
Oxygen toxicity
Trimix (breathing gas)Trimix

References


Footnotes


Further reading


External links


en.wikipedia.org