Deep 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, PADI define anything from 18 metres / 60 feet - 30 metres / 100 feet as a "deep dive" (other diving organisations vary)
• 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/180 metres dive

Deep Diving

Depth[nb 1]	Comments
40 feet/12 metres	Recreational diving limit for divers aged under 12 years old and beginner divers.
60 feet/18 metres	Recreational diving limit for divers with Open Water certification but without greater training and experience.
100 feet/30 metres	Recommended recreational diving limit for divers.[1] Average depth at which nitrogen narcosis symptoms begin to appear in adults.
130 feet/40 metres	Absolute recreational diving limit for divers specified by Recreational Scuba Training Council (RSTC).[1] Maximum depth reachable by a French level 2 diver accompanied by an instructor (level 4 diver), breathing air.
180 feet/55 metres	Technical diving limit for "extended range" dives breathing air to a maximum ppO2 of 1.4 ATA.
200 feet/60 metres	Maximum depth reachable by a French level 3 diver accompanied by another level 3 diver, breathing air.
218 feet/65 metres	Depth at which compressed air results in an unacceptable risk of oxygen toxicity.[nb 2]
330 feet/100 metres	Technical diving training limit for divers breathing trimix. Recommended technical diving limit.
509 feet/155 metres	Record depth for scuba dive on compressed air.[4]
660 feet/200 metres	Absolute limit for surface light penetration sufficient for plant growth, though minimal visibility possible farther down.[nb 3]
1,083 feet/330 metres	World record for deepest dive on SCUBA.[nb 4]
2,000 feet/610 metres	Navy diver in Atmospheric Diving System (ADS) suit .[5]

Particular problems associated with deep dives

Deep diving has more consequences and dangers than basic open water diving.^[6] Nitrogen narcosis, the “narks” or “rapture of the deep”, starts with feelings of euphoria and over-confidence but then leads to numbness and memory impairment similar to alcohol intoxication. Decompression sickness, or the “bends”, can happen if a diver ascends too fast, when excess inert gas leaves solution in the blood and tissues and forms bubbles. These bubbles produce mechanical and biochemical effects that lead to the condition. 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, and requires a recompression chamber for treatment. Deep diving involves a much greater danger of all of these, and presents the additional risk of oxygen toxicity, which may lead to a convulsion underwater. Very deep diving using a helium–oxygen mixture (heliox) carries a risk of high pressure nervous syndrome. Coping with the physical and physiological stresses of deep diving requires good physical conditioning.^[7]

Using normal scuba equipment, breathing gas consumption is proportional to ambient pressure - so at 50 metres (160 ft), where the pressure is 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, and gas becomes denser requiring increased effort to breathe with depth, leading to increasing risk of hypercapnia, an excess of carbon dioxide in the blood. The need to do decompression stops increases with depth. A diver at 6 metres (20 ft) may be able to dive for many hours without needing to do decompression stops. At depths greater than 40 metres (130 ft), 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. All of these considerations result in the amount of breathing gas required for deep diving being much greater than for shallow open water diving. The diver needs a disciplined approach to planning and conducting dives to minimise these additional risks.

Dealing with depth

Technical divers preparing for a mixed-gas decompression dive in Bohol, Philippines. Note the backplate and wing setup with sidemounted stage tanks containing EAN50 (left side) and pure oxygen (right side).

• 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

Verified SCUBA dives below 800 feet^{[citation needed]}

Name	Location	Depth	Year
Nuno Gomes	Red Sea Red Sea South Africa South Africa	1,044 feet (318 m) 890 feet (270 m) 927 feet (283 m) 826 feet (252 m)	2005 2004 1996 1994
Pascal Bernabé	Mediterranean Mediterranean	1,083 feet (330 m) 873 feet (266 m)	2005 2005
David Shaw[nb 5]	South Africa	888 feet (271 m)	2004
Gilberto M de Oliveira	Brazil	898 feet (274 m)	2002
John Bennett[nb 5]	Philippines Philippines	1,010 feet (310 m) 833 feet (254 m)	2001 2001
Jim Bowden	Mexico Mexico	925 feet (282 m) 825 feet (251 m)	1994 1993
Sheck Exley[nb 5]	South Africa Mexico	863 feet (263 m) 867 feet (264 m)	1993 1989
Don Shirley	South Africa	820 feet (250 m)	2005
Mark Ellyatt	Andaman Sea Thailand	1,026 feet (313 m) 850 feet (260 m)	2003 2003

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.^{[8][9][nb 6][10]} 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 five times since. Dives of this nature have been impossible to verify - proof being as tangible as faith more often than 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 claimed dives to depths of 260m and 313m.

Besides scuba, there is a small group of divers who have reached depths below 200 meters on closed-circuit rebreathers. Some examples are David Shaw, Don Shirley, Alessandro Scuotto, Marco Reis, Mario Marconi, Paul Raymeakers and Pim van der Horst.

Ultra deep air

While 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 astonishingly 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.^[11] From the comparatively few who survived extremely deep air dives:

• 1947 Frédéric Dumas, a colleague of Jacques Cousteau, dived to 307 feet (94 m) on air
• 1959 Ennio 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 dived to a depth of 452 feet (138 m) on air. Unusually, Gilliam remained largely functional at depth and was able to complete basic maths problems and answer simple questions written on a slate by his crew beforehand.
• 1993 Bret Gilliam extended his own world record to 475 feet (145 m), again reporting no ill effects from narcosis or oxygen toxicity.
• 1994 Dan Manion set the current record for a deep dive on air at 509 feet (155 m). Manion reported 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.^[when?]

See also

• Decompression sickness
• Breathing gas
• Free-diving, diving without breathing
• Heliox
• Hydreliox
• High pressure nervous syndrome
• Oxygen toxicity
• Trimix

References

1. ^ ^{a b c} Brylske, A. (2006). Encyclopedia of Recreational Diving, 3rd edition. United States: PADI. ISBN 1878663011. 
2. ^ Hydra 8: Pre-commercial Hydrogen Diving Project
3. ^ Comex S.A. HYDRA 8 and HYDRA 10 test projects
4. ^ 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.[1]
5. ^ Navy diver sets world record
6. ^ Egstrom GH (2006). "Historic Perspective: Scientific Deep Diving and the Management of the Risk". In: Lang, MA and Smith, NE (eds). Proceedings of Advanced Scientific Diving Workshop (Washington, DC). http://archive.rubicon-foundation.org/4653. Retrieved 2008-07-05. 
7. ^ Southerland, DG (2006). "Medical Fitness at 300 FSW". In: Lang, MA and Smith, NE (eds). Proceedings of Advanced Scientific Diving Workshop (Washington, DC). http://archive.rubicon-foundation.org/4659. Retrieved 2008-07-05. 
8. ^ Gomes, N. "Verified dives below 200 metres". http://www.nunogomes.co.za/rec.htm. Retrieved 2008-06-14. 
9. ^ Scubarecords.com. "Recorded Deep Dives Below 200 m". http://www.scubarecords.com/DeepRecords.htm. Retrieved 2008-06-14. 
10. ^ In 2007 Erdogan Bayburt, a former Turkish Navy diver, dived to a depth of 998 feet (304 m) 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.^{[citation needed]}
11. ^ Deep Diving, an advanced guide to physiology, procedures and systems. Bret Gilliam. 1995-01-25. ISBN 9780922769315. http://books.google.com/?id=HVbjgdorRXAC&pg=PT1&lpg=PT1&dq=Bret+Gilliam+deep+diving#v=onepage&q=&f=false. Retrieved 2009-11-19. 

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. Minimal visibility is still possible far deeper. Deep sea explorer William Beebe reported seeing blueness, not blackness, at 1400 feet (424 metres). "I peered down and again I felt the old longing to go farther, although it looked like the black pit-mouth of hell itself---yet still showed blue." (William Beebe, "A Round Trip to Davey Jones's Locker," The National Geographic Magazine, June 1931, p. 660.)
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