deep-sea diving

The meaning of the term deep diving is a form of technical diving.^[1] 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.^[2] 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.^[3] 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.

Diver returning from a 600 ft dive

Particular problems associated with deep dives

Deep diving obviously has more consequences and dangers than basic open water diving.^[5] 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 loss 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 conditioning.^[6]

• 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 air 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 tidal current, the divers may drift away from their boat cover or a safe exit point on the shore.
• Increased breathing effort. Gas becomes denser 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 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

Amongst technical divers, there are certain elite divers who participate in ultra-deep diving on SCUBA (using closed circuit rebreathers and heliox) below 660 feet (200 m). 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 800 feet (240 m) on self contained breathing apparatus recreationally.^{[7][8][nb 6][9]} That is fewer than the number of people who have walked on the surface of the moon. The Holy Grail of deep SCUBA diving was the 1,000 ft (300 m) mark, first achieved by John Bennett in 2001, and has only been achieved twice since.

In 2003 Mark Ellyatt is believed to have dived to a depth of 1,032 feet (315 m), but that dive has not been independently verified.

All of the foregoing dives were conducted on open circuit SCUBA equipment, except for David Shaw and 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.^[10] From the comparitively few who survived extremely deep air dives:

• 1947 Frederic Dumas, a colleague of Jacques Cousteau, dived to 307 feet (94 m) on air
• 1959 Ennie Falco reported having reached a depth of 435 feet (133 m) on air, but had no means to record it
• 1965 Tom Mount and Frank Martz dive to a depth of 360 feet (110 m) on air
• 1967 Hal Watts and AJ Muns dive to a depth of 390 feet (120 m) on air
• 1968 Neil Watson and John Gruener dived to 437 feet (133 m) 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 452 feet (138 m) 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 475 feet (145 m), again reporting no ill effects from narcosis or oxygen toxicity.
• 1994 Dan Manion sets current record for a deep dive on air at 509 feet (155 m). 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 Guiness 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

References

Footnotes

1. ^ All depths specified for sea water. Fractionally deeper depths may apply in relation to freshwater due to its lower density
2. ^ Oxygen toxicity depends upon a combination of partial pressure and time of exposure, individual physiology, and other factors not fully understood. NOAA recommends that divers do not expose themselves to breathing oxygen at greater than 1.6 bar ppO₂, which occurs at 218 feet breathing air.
3. ^ Assuming crystal clear water; surface light may disappear completely at much shallower depths in murky conditions.
4. ^ 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 earlier in the same year as the current official world record.
5. ^ ^{a b c} Subsequently died during diving accidents.
6. ^ 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 FSW which included a section on results from tests on the use of rebreathers at 850 feet. --Knafelc, ME (1989). "EX 19 Performance Testing at 850 and 450 FSW (Feet of Seawater).". US Naval Experimental Diving Unit Technical Report NEDU-8-89. http://archive.rubicon-foundation.org/7423. Retrieved 2008-07-24. 

Further reading

• Dent, W (2006). "AAUS Deep Diving Standards.". In: Lang, MA and Smith, NE (eds). Proceedings of Advanced Scientific Diving Workshop (Washington, DC). http://archive.rubicon-foundation.org/4669. Retrieved 2008-07-05. 

External links

• Recreational Deep Diving

v • d • e Underwater diving Types: Scuba diving · Surface supplied diving · Free-diving · Snorkelling · Saturation diving Specialities: Technical diving · Deep diving · Decompression diving · Mixed gas diving · Wreck diving · Cave diving · Ice diving · Rebreather diving · Solo diving · Altitude diving Equipment: Diving suit · Scuba set · Rebreather · Dive computer · Diver propulsion vehicle · Mask · Fins · Snorkel · Buoyancy control device Disciplines: Professional diving · Police diving · Military diving · Underwater photography · Underwater videography Hazards: Decompression sickness · Nitrogen narcosis · Oxygen toxicity · Barotrauma · Hyperbaric medicine · Drowning · Shallow water blackout · Deep water blackout · High pressure nervous syndrome · Dysbaric osteonecrosis