Underwater diving to a depth beyond the norm accepted by the associated community
Scuba diver using a rebreather with open circuit bailout cylinders returning from a 600-foot (180 m) dive
Deep diving is underwater diving to a depth beyond the norm accepted by the associated community. In some cases this is a prescribed limit established by an authority, while in others it is associated with a level of certification or training, and it may vary depending on whether the diving is recreational, technical or commercial. Nitrogen narcosis becomes a hazard below 30 metres (98 ft) and hypoxic breathing gas is required below 60 metres (200 ft) to lessen the risk of oxygen toxicity.
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.
Depth ranges in underwater diving
Assumed is the surface of the waterbody to be at or near sea level and underlies atmospheric pressure.
Not included are the differing ranges of freediving - without breathing during a dive.
Comex Hydra X (Hydra 10) simulated dive in an onshore hyperbaric chamber by Theo Mavrostomos on 20 November 1992.
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 rapidly, 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 six bar, a diver breathes six 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 increased 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.
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.
Scuba 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.
Hot-water suits can prevent hypothermia due to the high heat loss when using helium-based breathing gases.
Diving bells and lockoutsubmersibles expose the diver to the direct underwater environment for less time, and provide a relatively safe shelter that does not require decompression, with a dry environment where the diver can rest, take refreshment, and if necessary, receive first aid in an emergency.
Breathing gas reclaim systems reduce the cost of using helium-based breathing gases, by recovering and recycling exhaled surface supplied gas, analogous to rebreathers for scuba 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.
The most important procedure for dealing with physiological problems of breathing at high ambient pressures associated with deep diving is decompression. This is necessary to prevent inert gas bubble formation in the body tissues of the diver, which can cause severe injury. Decompression procedures have been derived for a large range of pressure exposures, using a large range of gas mixtures. These basically entail a slow and controlled reduction in pressure during ascent by using a restricted ascent rate and decompression stops, so that the inert gases dissolved in the tissues of the diver can be eliminated harmlessly during normal respiration.
Gas management procedures are necessary to ensure that the diver has access to suitable and sufficient breathing gas at all times during the dive, both for the planned dive profile and for any reasonably foreseeable contingency. Scuba gas management is logistically more complex than surface supply, as the diver must either carry all the gas, must follow a route where previously arranged gas supply depots have been set up (stage cylinders). or must rely on a team of support divers who will provide additional gas at pre-arranged signals or points on the planned dive. On very deep scuba dives or on occasions where long decompression times are planned, it is a common practice for support divers to meet the primary team at decompression stops to check if they need assistance, and these support divers will often carry extra gas supplies in case of need. The use of rebreathers can reduce the bulk of the gas supplies for long and deep scuba dives, at the cost of more complex equipment with more potential failure modes, requiring more complex procedures and higher procedural task loading.
Surface supplied diving distributes the task loading between the divers and the support team, who remain in the relative safety and comfort of the surface control position. Gas supplies are limited only by what is available at the control position, and the diver only needs to carry sufficient bailout capacity to reach the nearest place of safety, which may be a diving bell or lockout submersible.
Saturation diving is a procedure used to reduce the high-risk decompression a diver is exposed to during a long series of deep underwater exposures. By keeping the diver under high pressure for the whole job, and only decompressing at the end of several days to weeks of underwater work, a single decompression can be done at a slower rate without adding much overall time to the job. During the saturation period, the diver lives in a pressurized environment at the surface, and is transported under pressure to the underwater work site in a closed diving bell.
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 thirty-five people are known to have ever dived below a depth of 240 metres (790 ft) on self-contained breathing apparatus recreationally.[nb 4][nb 5] 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 seven times since.
The difficulties involved in 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 lead 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 that confront divers engaging in ultra-deep diving on self-contained breathing apparatus include:
There are no reliable decompression algorithms tested for such depths on the assumption of an immediate surfacing. Almost all decompression methodology for such depths is based upon saturation, and calculates ascent times in days rather than hours. Accordingly, ultra-deep dives are almost always a partly experimental basis.
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.
A severe risk in ultra-deep air diving is deep water blackout, or depth blackout, a loss of consciousness at depths below 50 m with no clear primary cause, associated with nitrogen narcosis, a neurological impairment with anaesthetic effects caused by high partial pressure of nitrogen dissolved in nerve tissue, and possibly acute oxygen toxicity. The term is not in widespread use at present, as where the actual cause of blackout is known, a more specific term is preferred. The depth at which deep water blackout occurs is extremely variable and unpredictable.
Before the popular availability of Trimix, attempts were made to set world record depths using air. The extreme risk of both narcosis and oxygen toxicity in the divers contributed to a high fatality rate in 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:
1959—Ennio Falco reported having reached a depth of approximately 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 fsw 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.
1971—Sheck Exley dived to 142 metres (466 ft) on air on 11 December near Andros Island in the Bahamas. Exley was only supposed to go down to 91 metres (299 ft) in his capacity as a safety diver (although he had practised several dives to 120 metres (390 ft) in preparation), but descended to search for the dive team after they failed to return on schedule. Exley almost made it to the divers, but was forced to turn back due to heavy narcosis and nearly blacking out.
1990—Bret Gilliam dived to a depth of 452 fsw 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 fsw, 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 fsw. 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 in mid-2005.
Fatalities during depth record attempts
Maurice Fargues died in 1947 in an experiment to see how deep a scuba diver could go. He reached 120 m before failing to return line signals.
Hope Root died December 1953 trying to break the deep diving record of 330 feet; he was last seen passing 625 feet.
Archie Forfar and Anne Gunderson died on 11 December 1971 off the coast of Andros Island, Bahamas, while attempting to dive to 480 feet, which would have been the world record at the time. Their third team member, Jim Lockwood, only survived due to his use of a safety weight that dropped when he lost consciousness, causing him to start an uncontrolled ascent before being intercepted by a safety diver at a depth of around 300 foot. As mentioned above, Sheck Exley, who was acting as another safety diver at 300 feet, inadvertently managed to set the depth record when he descended towards Forfar and Gunderson, who were both still alive at the 480-foot level, although completely incapacitated by narcosis. Exley was forced to give up his attempt at around 465 feet deep when the narcosis very nearly overcame him as well. The bodies of Forfar and Gunderson were never recovered.
Sheck Exley died in 1994 in an attempt to reach the bottom of Zacatón in a dive that would have extended his own world record (at the time) for deep diving.
Dave Shaw died in 2005 in an attempt at the deepest ever body recovery and deepest ever dive on a rebreather.
Brigitte Lenoir, planning to attempt the deepest dive ever made by a woman, died in 2010 in Dahab (Egypt) during a training dive.
Guy Garman died on 15 August 2015 in an unsuccessful attempt to dive to 1,200 feet (370 m). The Virgin Island Police Department confirmed that Dr. Guy Garman's body was recovered on 18 August 2015.
Theodora Balabanova died at Toroneos Bay, Greece, on 27 September 2017 attempting to beat the women's deep dive record. She did not complete the decompression stops and surfaced too early.
Waclaw Lejko attempting 275 m / 902 ft in Lake Garda, died on 27 September 2017. His body was recovered with a ROV at 230 m / 754 ft.
Adam Krzysztof Pawlik, attempting a 316 m dive in Lake Garda, died on 18 October 2018. His body was located at 284 meters.
Sebastian Marczewski, attempting a 333 m dive in Lake Garda, reached the target depth of 333 m but his tanks became entangled in his ascent line at 150 m. He died on 6 July 2019.
Oxygen toxicity – Toxic effects of breathing in oxygen at high concentrations
Trimix – Breathing gas consisting of oxygen, helium and nitrogen
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^Set by Dr Dan Marion on 18 March 1994. The record is not officially recognised anywhere, and 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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^All depths specified for sea water. Fractionally deeper depths may apply in relation to freshwater due to its lower density
^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 pO2, which occurs at 66 metres (217 ft) when breathing air.
^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.)
^Statistics exclude military divers (classified), and commercial divers (commercial diving to those depths on scuba is not permitted by occupational health and safety legislation). 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 that 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 Navy Experimental Diving Unit Technical Report. NEDU-8-89. Retrieved 24 July 2008.
^In 2007 a 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.
^ abcdefgSubsequently died during diving accidents.
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