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Deep diving has different meanings depending on the context. Even in recreational diving the meaning may vary:
Contents
- Particular problems associated with deep dives
- Dealing with depth
- Equipment adaptations for deeper diving
- Procedural adaptations for deeper diving
- Ultra deep diving
- Ultra deep air
- Fatalities during depth record attempts
- References
In recreational diving, a depth below about 30 metres (98 ft), where nitrogen narcosis becomes a significant hazard for some divers, may be considered a "deep dive".
For some recreational diving agencies, Deep diving, or Deep diver may be a certification awarded to divers that have been trained to dive to a specified depth range, generally deeper than 30 metres (98 ft). However, the Professional Association of Diving Instructors (PADI) defines anything from 18 metres (60 ft) to 30 metres (100 ft) as a "deep dive" in the context of recreational diving (other diving organisations vary), and considers deep diving a form of technical diving.
In technical diving, a depth below about 60 metres (200 ft) where hypoxic breathing gas becomes necessary to avoid oxygen toxicity may be considered a "deep dive".
In professional diving, a depth that requires special equipment, procedures, or advanced training may be considered a deep dive.
Deep diving can mean something else in the commercial diving field. For instance early experiments carried out by Comex S.A. (Compagnie maritime d'expertises) using hydrox and trimix attained far greater depths than any recreational technical diving. One example being the Comex Janus IV open-sea dive to 501 metres (1,644 ft) in 1977. The open-sea diving depth record was achieved in 1988 by a team of Comex divers who performed pipeline connection exercises at a depth of 534 metres (1,752 ft) 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 2,000 feet (610 m). 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.
Particular problems associated with deep dives
Deep diving has more hazards and greater risk than basic open water diving. 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 onset of symptoms depends on the severity of the tissue gas loading and may develop during ascent in severe cases, but is frequently delayed until after reaching the surface. Bone degeneration (dysbaric osteonecrosis) is caused by the bubbles forming inside the bones; most commonly the upper arm and the thighs. 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.
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 makes the diver breathe even more gas, 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.
Many of these problems are avoided by the use of surface supplied breathing gas, closed diving bells, and saturation diving, at the cost of logistical complexity, reduced maneuverability of the diver and greater expense.
Dealing with depth
Both equipment and procedures can be adapted to deal with the problems of greater depth. Usually the two are combined, as the procedures must be adapted to suit the equipment, and in some cases the equipment is needed to facilitate the procedures.
Equipment adaptations for deeper diving
The equipment used for deep diving depends on both the depth and the type of diving. Scuba is limited to equipment that can be carried by the diver, or is easily deployed by the dive team, while surface supplied diving equipment can be more extensive, and much of it stays above the water where it is operated by the support team.
Procedural adaptations for deeper diving
Procedural adaptations for deep diving can be classified as those procedures for operating specialized equipment, and those that apply directly to the problems caused by exposure to high ambient pressures.
Ultra-deep diving
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.
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.
Serious issues which confront divers engaging in ultra-deep diving on self-contained breathing apparatus include:
In addition, "ordinary" risks like gas reserves, hypothermia, dehydration and oxygen toxicity are compounded by extreme depth and exposure. Much technical equipment is simply not designed for the necessarily greater stresses at depths, and reports of key equipment (including submersible pressure gauges) imploding are not uncommon.
Verna van Schaik in 2004 set the Guinness Woman's World Record for the deepest dive with a dive to 221 metres (725 ft) in Boesmansgat cave.
Claudia Serpieri in 2000 reached 211 metres (692 ft), the deepest sea dive by a woman.
Tatiana Oparina in 2015, reached 156 m in Lake Baikal, the deepest dive in extreme cold water (+3C) by a woman.
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 contributed to a 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 comparatively few who survived extremely deep air dives:
In deference to the high death rate, the Guinness World Records ceased to publish records on deep air dives in mid-2005.