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, 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"

[edit] Particular problems associated with deep dives

Deep diving obviously has more consequences and dangers than basic open water diving.^[2] 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 harms and possibly worse effects of deep diving. These physical and physiological stresses require good physical conditioning.^[3]

• 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 carbon dioxide poisoning.
• Oxygen toxicity.
• High pressure nervous syndrome.

[edit] Dealing with depth

• Carry larger volumes of breathing gas to compensate for the increased gas consumption and decompression stops.
• Rebreathers are much more efficient consumers of gas than open circuit scuba and inherently more complex than open circuit scuba.
• Use helium-based breathing gases such as trimix to reduce nitrogen narcosis and stay beyond 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.

[edit] 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 metres. 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 on self contained breathing apparatus recreationally.^{[4][5][nb 5]} That is fewer than the number of people who have walked on the surface of the moon. The Holy Grail of deep diving was the 1000 ft. 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, but that dive has not been independently verified.

All of the foregoing dives were conducted on open circuit SCUBA equipment, except for David Shaw, who used a closed-circuit rebreather.

[edit] See also

• Decompression sickness
• Breathing gas
• Heliox
• Hydreliox
• High pressure nervous syndrome
• Oxygen toxicity
• Trimix

[edit] References

[edit] 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 1,056 feet dive by Nuno Gomes (diver) earlier in the same year as the current official world record.
5. ^ 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 on 24 July 2008. 
6. ^ ^{a b c d} Subsequently died during diving accidents.

[edit] 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 on 5 July 2008. 

[edit] External links

• Recreational Deep Diving