Deep diving

Depth ranges in underwater diving

Particular problems associated with deep dives

Limiting factors

Dealing with depth

Equipment adaptations for deeper diving

• Scuba divers carry larger volumes of breathing gas to compensate for the increased gas consumption and decompression stops.
• Rebreathers, though more complex, manage gas much more efficiently than open-circuit scuba.
• Use of helium-based breathing gases such as trimix reduces nitrogen narcosis and reduces the toxic effects of oxygen at depth.
• A diving shot, a decompression trapeze, or a decompression buoy can help divers control their ascent and return to the surface at a position that 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 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 s 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

• 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. 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.

• Rebreather diving 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 demanding 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

Mixed gas

Air

Risk

Gas density and work of breathing

Decompression schedules

Narcosis and HPNS

Inner ear decompression sickness

Thermal stress

Gas logistics

Psychological issues

• Risk denial
• Target fixation
• Dunning–Kruger effect
• Sunk cost

  Statistics

• Number of successful depth record attempts:
• Number of non-fatal failed depth record attempts:
• Number of fatal depth record attempts:

  Fatalities during depth record attempts

• Maurice Fargues, a member of the GRS, died in 1947 after losing consciousness at depth in an experiment to see how deep a scuba diver could go. He reached before failing to return line signals. He became the first diver to die while using an Aqua-Lung.
• Hope Root died on 3 December 1953 off the coast of Miami Beach trying set a deep diving record of with an Aqua-Lung; he passed and was not seen again.
• Archie Forfar and Ann Gunderson died on 11 December 1971 off the coast of Andros Island, while attempting to dive to, 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 at, causing him to start an uncontrolled ascent before being intercepted by a safety diver at a depth of around. 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 when the narcosis very nearly overcame him as well. The bodies of Forfar and Gunderson were never recovered.
• Sheck Exley died in 1994 at in an attempt to reach the bottom of Zacatón in a dive that would have extended his own world record for deep diving.
• Dave Shaw died in 2005 in an attempt at the deepest ever body recovery and deepest ever dive on a rebreather at.The incident was triggered by difficulties managing the body, which led to overexertion and irreversible hypercapnia due to high work of breathing, possibly aggravated by negative pressure breathing.
• Brigitte Lenoir, planning to attempt the deepest dive ever made by a woman with a rebreather to, died on 14 May 2010 in Dahab while ascending from a training dive at.
• Guy Garman died on 15 August 2015 in an unsuccessful attempt to dive to. The Virgin Island Police Department confirmed that Guy Garman's body was recovered on 18 August 2015.
• Theodora Balabanova died at Toroneos Bay, Greece, in September 2017 attempting to break the women's deep dive record with. She did not complete the decompression stops and surfaced too early.
• Wacław Lejko attempting in Lake Garda, died in September 2017. His body was recovered with an ROV at.
• Adam Krzysztof Pawlik, attempting to break the deep-diving world record of by Jarek Macedoński in Lake Garda, died on 13 October 2018. His body was located at.
• Sebastian Marczewski was attempting to break the deep-diving world record going below in Lake Garda. He died on 6 July 2019 at.
• Han Ting, having renewed his own deepest Asian cave dive record to in April 2023 in Tianchuang, planned to set a world record for deepest cave dive there, aiming at on 12 October 2023. He failed to return from a preparatory dive on 7 October. His body was recovered by an ROV on 25 October 2023.