Deep diving

Updated on Dec 18, 2023

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Deep diving has different meanings depending on the context. Even in recreational diving the meaning may vary:

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.

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.

A diving shot, a decompression trapeze or a decompression buoy can help divers control their ascent and return to the surface at a position which can be monitored by their surface support team at the end of a dive.

Decompression can be accelerated by using specially blended breathing gas mixtures containing lower proportions of inert gas.

Surface supply of breathing gases reduces the risk of running out of gas.

In-water decompression can be minimized by using dry bells and decompression chambers.

Hot-water suits can prevent hypothermia due to the high heat loss when using helium based breathing gases.

Diving bells and lockout submersibles 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.

The most radical equipment adaptation for deep diving is to isolate the diver from the direct pressure of the environment, using armoured atmospheric diving suits that allow diving to depths beyond those currently possible at ambient pressure. These rigid, articulated exoskeleton suits are sealed against water and withstand external pressure while providing life support to the diver for several hours at an internal pressure of approximately normal surface atmospheric pressure. This avoids the problems of inert gas narcosis, decompression sickness, barotrauma, oxygen toxicity, high work of breathing, compression arthralgia, high-pressure nervous syndrome and hypothermia, but at the cost of reduced mobility and dexterity, logistical problems due to the bulk and mass of the suits, and high equipment costs.

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.

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.

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:

High-pressure nervous syndrome (HPNS). HPNS, brought on by breathing helium under extreme pressure causes tremors, myoclonic jerking, somnolence, EEG changes, visual disturbance, nausea, dizziness, and decreased mental performance. Symptoms of HPNS are exacerbated by rapid compression, a feature common to ultra-deep "bounce" dives.

Decompression algorithm. 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.

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:

1947 Frédéric Dumas, a colleague of Jacques Cousteau, dived to 94 metres (308 ft) on air

1947 Maurice Fargues, another colleague of Jacques Cousteau, dived to 117 metres (384 ft) on air but died after losing consciousness at depth

1957 Eduard Admetlla i Lázaro descended to 100 meters on air

1959 Ennio Falco reported having reached a depth of 133 metres (436 ft) on air, but had no means to record it

1965 Tom Mount and Frank Martz dive to a depth of 110 metres (360 ft) on air

1967 Hal Watts and AJ Muns dive to a depth of 120 metres (390 ft) on air

1968 Neil Watson and John Gruener dived to 133 metres (436 ft) 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 December 11 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 138 metres (453 ft) 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 145 metres (476 ft), again reporting no ill effects from narcosis or oxygen toxicity.

1994 Dan Manion set the current record for a deep dive on air at 155 metres (509 ft). 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.

Hope Root died December 1953 trying to break the deep diving record of 330 feet; he was last seen passing 625 feet.

Sheck Exley died in 1994 in an attempt to reach the bottom of Zacatón in a dive that would have extend 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.

Guy Garman died on August 15, 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 late Tuesday August 18, 2015.

References

Deep diving Wikipedia

(Text) CC BY-SA

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