Portal:Underwater diving

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Portal:Underwater diving

Shore entry and exit area at Shark Alley, Miller's Point, South Africa
Topic definition

Underwater diving can be described as all of the following:

  • A human activity – intentional, purposive, conscious and subjectively meaningful sequence of actions. Underwater diving is practiced as part of an occupation, or for recreation, where the practitioner submerges below the surface of the water or other liquid for a period which may range between seconds to the order of a day at a time, either exposed to the ambient pressure or isolated by a pressure resistant suit, to interact with the underwater environment for pleasure, competitive sport, or as a means to reach a work site for profit or in the pursuit of knowledge, and may use no equipment at all, or a wide range of equipment which may include breathing apparatus, environmental protective clothing, aids to vision, communication, propulsion, maneuverability, buoyancy and safety equipment, and tools for the task at hand.
Portal scope

The scope of this portal includes the technology supporting diving activities, the physiological and medical aspects of diving, the skills and procedures of diving and the training and registration of divers, underwater activities which are to some degree dependent on diving, economical, commercial, safety, and legal aspects of diving, biographical information on notable divers, inventors and manufacturers of diving related equipment and researchers into aspects of diving.

Introduction to underwater diving
 Two divers wearing lightweight demand helmets stand back-to-back on an underwater platform holding on to the railings. The photo also shows the support vessel above the surface in the background.
Surface-supplied divers riding a stage to the underwater workplace


Underwater diving, as a human activity, is the practice of descending below the water's surface to interact with the environment.

Immersion in water and exposure to high ambient pressure have physiological effects that limit the depths and duration possible in ambient pressure diving. Humans are not physiologically and anatomically well adapted to the environmental conditions of diving, and various equipment has been developed to extend the depth and duration of human dives, and allow different types of work to be done.


In ambient pressure diving, the diver is directly exposed to the pressure of the surrounding water. The ambient pressure diver may dive on breath-hold, or use breathing apparatus for scuba diving or surface-supplied diving, and the saturation diving technique reduces the risk of decompression sickness (DCS) after long-duration deep dives. Atmospheric diving suits (ADS) may be used to isolate the diver from high ambient pressure. Crewed submersibles can extend depth range, and remotely controlled or robotic machines can reduce risk to humans.


The environment exposes the diver to a wide range of hazards, and though the risks are largely controlled by appropriate diving skills, training, types of equipment and breathing gases used depending on the mode, depth and purpose of diving, it remains a relatively dangerous activity.

Diving activities are restricted to maximum depths of about 40 metres (130 ft) for recreational scuba diving, 530 metres (1,740 ft) for commercial saturation diving, and 610 metres (2,000 ft) wearing atmospheric suits. Diving is also restricted to conditions which are not excessively hazardous, though the level of risk acceptable can vary.


Recreational diving (sometimes called sport diving or subaquatics) is a popular leisure activity. Technical diving is a form of recreational diving under especially challenging conditions. Professional diving (commercial diving, diving for research purposes, or for financial gain) involve working underwater. Public safety diving is the underwater work done by law enforcement, fire rescue, and underwater search and recovery dive teams. Military diving includes combat diving, clearance diving and ships husbandry.

Deep sea diving is underwater diving, usually with surface supplied equipment, and often refers to the use of standard diving dress with the traditional copper helmet. Hard hat diving is any form of diving with a helmet, including the standard copper helmet, and other forms of free-flow and lightweight demand helmets.

The history of breath-hold diving goes back at least to classical times, and there is evidence of prehistoric hunting and gathering of seafoods that may have involved underwater swimming. Technical advances allowing the provision of breathing gas to a diver underwater at ambient pressure are recent, and self-contained breathing systems developed at an accelerated rate following the Second World War. Read more...

Diving mode articles

Randomly selected diving mode article

Picture taken of the Battlespace Preparation Autonomous Underwater Vehicle (BPAUV) by an employee of Bluefin Robotics Corporation during a US Navy exercise.

An autonomous underwater vehicle (AUV) is a robot that travels underwater without requiring input from an operator. AUVs constitute part of a larger group of undersea systems known as unmanned underwater vehicles, a classification that includes non-autonomous remotely operated underwater vehicles (ROVs) – controlled and powered from the surface by an operator/pilot via an umbilical or using remote control. In military applications a AUV is more often referred to as unmanned undersea vehicle (UUV). Underwater gliders are a subclass of AUVs. Read more...

Picture taken of the Battlespace Preparation Autonomous Underwater Vehicle (BPAUV) by an employee of Bluefin Robotics Corporation during a US Navy exercise.

An autonomous underwater vehicle (AUV) is a robot that travels underwater without requiring input from an operator. AUVs constitute part of a larger group of undersea systems known as unmanned underwater vehicles, a classification that includes non-autonomous remotely operated underwater vehicles (ROVs) – controlled and powered from the surface by an operator/pilot via an umbilical or using remote control. In military applications a AUV is more often referred to as unmanned undersea vehicle (UUV). Underwater gliders are a subclass of AUVs. Read more...

Diving and support equipment

Randomly selected diving or support equipment article

Israeli Navy Underwater Missions Unit transfers equipment using lifting-bags

A lifting bag is an item of diving equipment consisting of a robust and air-tight bag with straps, which is used to lift heavy objects underwater by means of the bag's buoyancy. The heavy object can either be moved horizontally underwater by the diver or sent unaccompanied to the surface.

Lift bag appropriate capacity should match the task at hand. If the lift bag is grossly oversized a runaway or otherwise out of control ascent may result. Commercially available lifting bags may incorporate dump valves to allow the operator to control the buoyancy during ascent, but this is a hazardous operation with high risk of entanglement in an uncontrolled lift or sinking. If a single bag is insufficient, multiple bags may be used, and should be distributed to suit the load.

There are also lifting bags used on land as short lift jacks for lifting cars or heavy loads or lifting bags which are used in machines as a type of pneumatic actuator which provides load over a large area. These lifting bags of the AS/CR type are for example used in the brake mechanism of rollercoasters. Read more...

Diving procedure articles

Randomly selected diving procedure article

A group of divers seen from below. Two are holding onto the anchor cable as an aid to depth control during a decompression stop.

The practice of decompression by divers comprises the planning and monitoring of the profile indicated by the algorithms or tables of the chosen decompression model, to allow asymptomatic and harmless release of excess inert gases dissolved in the tissues as a result of breathing at ambient pressures greater than surface atmospheric pressure, the equipment available and appropriate to the circumstances of the dive, and the procedures authorized for the equipment and profile to be used. There is a large range of options in all of these aspects.

Decompression may be continuous or staged, where the ascent is interrupted by stops at regular depth intervals, but the entire ascent is part of the decompression, and ascent rate can be critical to harmless elimination of inert gas. What is commonly known as no-decompression diving, or more accurately no-stop decompression, relies on limiting ascent rate for avoidance of excessive bubble formation. Staged decompression may include deep stops depending on the theoretical model used for calculating the ascent schedule. Omission of decompression theoretically required for a dive profile exposes the diver to significantly higher risk of symptomatic decompression sickness, and in severe cases, serious injury or death. The risk is related to the severity of exposure and the level of supersaturation of tissues in the diver. Procedures for emergency management of omitted decompression and symptomatic decompression sickness have been published. These procedures are generally effective, but vary in effectiveness from case to case.

The procedures used for decompression depend on the mode of diving, the available equipment, the site and environment, and the actual dive profile. Standardized procedures have been developed which provide an acceptable level of risk in the circumstances for which they are appropriate. Different sets of procedures are used by commercial, military, scientific and recreational divers, though there is considerable overlap where similar equipment is used, and some concepts are common to all decompression procedures. Read more...

Diving science

Randomly selected diving science article

Work of breathing (WOB) is the energy expended to inhale and exhale a breathing gas. It is usually expressed as work per unit volume, for example, joules/litre, or as a work rate (power), such as joules/min or equivalent units, as it is not particularly useful without a reference to volume or time. It can be calculated in terms of the pulmonary pressure multiplied by the change in pulmonary volume, or in terms of the oxygen consumption attributable to breathing. In a normal resting state the work of breathing constitutes about 5% of the total body oxygen consumption. It can increase considerably due to illness or constraints on gas flow imposed by breathing apparatus, ambient pressure, or breathing gas composition. Read more...

Occupational diving articles

Randomly selected occupational diving article

Diver wearing a diving helmet is sanding a repair patch on a submarine

Professional diving is diving where the divers are paid for their work. There are several branches of professional diving, the best known of which is probably commercial diving and its specialised applications, offshore diving, inshore civil engineering diving, marine salvage diving, HAZMAT diving, and ships husbandry diving. There are also applications in scientific research, Marine archaeology, fishing and aquaculture, public service and law enforcement and military service. Any person wishing to become a professional diver normally requires specific training that satisfies any regulatory agencies which have regional or national authority, such as US Occupational Safety and Health Administration, United Kingdom Health and Safety Executive or South African Department of Labour. Due to the dangerous nature of some professional diving operations, specialized equipment such as an on-site hyperbaric chamber and diver-to-surface communication system is often required by law. Read more...

Recreational diving articles

Randomly selected recreational diving article

Trevor Jackson returns from SS Kyogle.jpg

Technical diving (also referred to as tec diving or tech diving) is scuba diving that exceeds the agency-specified limits of recreational diving for non-professional purposes. Technical diving may expose the diver to hazards beyond those normally associated with recreational diving, and to greater risk of serious injury or death. The risk may be reduced by appropriate skills, knowledge and experience, and by using suitable equipment and procedures. The skills may be developed through appropriate specialised training and experience. The equipment often involves breathing gases other than air or standard nitrox mixtures, and multiple gas sources.

The term technical diving has been credited to Michael Menduno, who was editor of the (now defunct) diving magazine aquaCorps Journal. The concept and term, technical diving, are both relatively recent advents, although divers have been engaging in what is now commonly referred to as technical diving for decades. Read more...

Diving hazards, incidents, safety and law articles

Randomly selected diving safety article

US Navy 030311-N-5362A-005 Members of Underwater Construction Team Two (UCT-2) listen to a safety brief from their dive supervisor.jpg

The diving supervisor is the professional diving team member who is directly responsible for the diving operation's safety and the management of any incidents or accidents that may occur during the operation; the supervisor is required to be available at the control point of the diving operation for the diving operation's duration, and to manage the planned dive and any contingencies that may occur. Details of competence, requirements, qualifications, registration and formal appointment differ depending on jurisdiction and relevant codes of practice. Diving supervisors are used in commercial diving, military diving, public safety diving and scientific diving operations.

The control point is the place where the supervisor can best monitor the status of the diver and progress of the dive. For scuba dives this is commonly on deck of the dive boat where there is a good view of the surface above the operational area, or on the shore at a nearby point where the divers can be seen when surfaced. For surface supplied diving, the view of the water is usually still necessary, and a view of the line tenders handling the umbilicals is also required, unless there is live video feed from the divers and two-way audio communications with the tenders. The control position also includes the gas panel and communications panel, so the supervisor can remain as fully informed as practicable of the status of the divers and their life support systems during the dive. For bell diving and saturation diving the situation is more complex and the control position may well be inside a compartment where the communications, control and monitoring equipment for the bell and life-support systems are set up.

In recreational diving the term is used to refer to persons managing a recreational dive, with certification such as Divemaster, Dive Control Specialist, Dive Coordinator, etc. Read more...

Diving medicine, disorders and treatment articles

Randomly selected diving medicine article

HyperBaric Oxygen Therapy Chamber 2008.jpg

Hyperbaric medicine is medical treatment in which an ambient pressure greater than sea level atmospheric pressure is a necessary component. The treatment comprises hyperbaric oxygen therapy (HBOT), the medical use of oxygen at an ambient pressure higher than atmospheric pressure, and therapeutic recompression for decompression illness, intended to reduce the injurious effects of systemic gas bubbles by physically reducing their size and providing improved conditions for elimination of bubbles and excess dissolved gas.

The equipment required for hyperbaric oxygen treatment consists of a pressure chamber, which may be of rigid or flexible construction, and a means of delivering 100% oxygen. Operation is performed to a predetermined schedule by trained personnel who monitor the patient and may adjust the schedule as required. HBOT found early use in the treatment of decompression sickness, and has also shown great effectiveness in treating conditions such as gas gangrene and carbon monoxide poisoning. More recent research has examined the possibility that it may also have value for other conditions such as cerebral palsy and multiple sclerosis, but no significant evidence has been found.

Therapeutic recompression is usually also provided in a hyperbaric chamber. It is the definitive treatment for decompression sickness and may also be used to treat arterial gas embolism caused by pulmonary barotrauma of ascent. In emergencies divers may sometimes be treated by in-water recompression if a chamber is not available and suitable diving equipment to reasonably secure the airway is available.

A number of hyperbaric treatment schedules have been published over the years for both therapeutic recompression and hyperbaric oxygen therapy for other conditions. Read more...

Underwater tools and weapons articles

Randomly selected underwater tools or weapon article

A limpet mine is a type of naval mine attached to a target by magnets. It is so named because of its superficial similarity to the limpet, a type of sea snail that clings tightly to rocks or other hard surfaces.

A swimmer or diver may attach the mine, which is usually designed with hollow compartments to give the mine slight negative buoyancy, making it easier to handle underwater.

Usually limpet mines are set off by a time fuse. They may also have an anti-handling device, making the mine explode if removed from the hull by enemy divers or by explosions. Sometimes the limpet mine was fitted with a small turbine which would detonate the mine after the ship had sailed a certain distance, so that it was likely to sink in navigable channels or deep water out of reach of easy salvage and making it harder to find what caused the sinking. Read more...

History of diving articles

Randomly selected diving history article

Alexander the Great diving NOAA.jpg

The history of underwater diving starts with freediving as a widespread means of hunting and gathering, both for food and other valuable resources such as pearls and coral, By classical Greek and Roman times commercial applications such as sponge diving and marine salvage were established, Military diving also has a long history, going back at least as far as the Peloponnesian War, with recreational and sporting applications being a recent development. Technological development in ambient pressure diving started with stone weights (skandalopetra) for fast descent. In the 16th and 17th centuries diving bells became functionally useful when a renewable supply of air could be provided to the diver at depth, and progressed to surface supplied diving helmets - in effect miniature diving bells covering the diver's head and supplied with compressed air by manually operated pumps - which were improved by attaching a waterproof suit to the helmet and in the early 19th century became the standard diving dress.

Limitations in mobility of the surface supplied systems encouraged the development of both open circuit and closed circuit scuba in the 20th century, which allow the diver a much greater autonomy. These also became popular during World War II for clandestine military operations, and post-war for scientific, search and rescue, media diving, recreational and technical diving. The heavy free-flow surface supplied copper helmets evolved into lightweight demand helmets, which are more economical with breathing gas, which is particularly important for deeper dives and expensive helium based breathing mixtures, and saturation diving reduced the risks of decompression sickness for deep and long exposures.

An alternative approach was the development of the "single atmosphere" or armoured suit, which isolates the diver from the pressure at depth, at the cost of great mechanical complexity and limited dexterity. The technology first became practicable in the middle 20th century. Isolation of the diver from the environment was taken further by the development of remotely operated underwater vehicles in the late 20th century, where the operator controls the ROV from the surface, and autonomous underwater vehicles, which dispense with an operator altogether. All of these modes are still in use and each has a range of applications where it has advantages over the others, though diving bells have largely been relegated to a means of transport for surface supplied divers. In some cases combinations are particularly effective, such as the simultaneous use of surface orientated or saturation surface supplied diving equipment and work or observation class remotely operated vehicles.

Although the pathophysiology of decompression sickness in not yet fully understood, decompression practice has reached a stage where the risk is fairly low, and most incidences are successfully treated by therapeutic recompression and hyperbaric oxygen therapy. Mixed breathing gases are routinely used to reduce the effects of the hyperbaric environment on ambient pressure divers. Read more...

Diving salvage operations articles

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1783, Royal George medallion.png

Initial attempts

Several attempts were made to raise the vessel, both for salvage and because she was a major hazard to navigation, lying in a busy harbour at a depth of only 65 ft (20 m).

In 1782, Charles Spalding recovered six iron 12-pounder guns and nine brass 12-pounders using a diving bell of his design. Read more...

Combat and clandestine frogman operations articles

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Amtrack-82.jpg

On 2 April 1982, Argentine forces launched the invasion of the Falkland Islands (Spanish: Islas Malvinas), beginning the Falklands War. The Argentines mounted amphibious landings, and the invasion ended with the surrender of Government House. Read more...

Diver training, registration and certification articles

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PADI-Ausbildungssystem.svg
A Divemaster (DM) is a recreational diving role which includes organising and leading recreational dives, particularly in a professional capacity, and is a qualification used throughout most of the world in recreational scuba diving for a diver who has supervisory responsibility for a group of divers and as a dive guide. As well as being a generic term, Divemaster is the title of the first professional rating of many training agencies, such as PADI, SSI, SDI, NASE, except NAUI, which rates a NAUI Divemaster just under an Instructor but above an Assistant Instructor. The Divemaster certification is generally equivalent to the requirements of international Standard ISO 24801-3 Dive Leader.

The BSAC recognizes several agencies' Divemaster certificates as equivalent to BSAC Dive Leader, but not to BSAC Advanced Diver. The converse may not be true.

The certification is a prerequisite for training as an instructor in recreational diving with most agencies except NAUI, where it is an optional step, because of the different position of the NAUI Divemaster in the NAUI hierarchy. Read more...

Diving related organisations articles

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Confédération Mondiale des Activités Subaquatiques (CMAS) is an international federation that represents underwater activities in underwater sport and underwater sciences, and oversees an international system of recreational snorkel and scuba diver training and recognition. It is also known by its English name, the World Underwater Federation, and its Spanish name, Confederacion Mundial De Actividades Subacuaticas. Its foundation in Monaco during January 1959 makes it one of the world's oldest underwater diving organisations. Read more...

Diving related publications articles

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The NOAA Diving Manual: Diving for Science and Technology is a book originally published by the US Department of Commerce for use as training and operational guidance for National Oceanographic and Atmospheric Administration divers. Several editions have been published, and several editors and authors have contributed over the years. The book is widely used as a reference work by professional and recreational divers. Read more...

Diving related biographies

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Karen Kohanowich.jpg

Karen Kohanowich is the Undersea Technology Officer for the Office of Ocean Exploration and Research (OER), a division of the Office of Oceanic and Atmospheric Research (OAR) at the National Oceanic and Atmospheric Administration (NOAA). She was NOAA's Acting Director of the National Undersea Research Program (NURP) from 2006-2009. In July 2006, she served as an aquanaut on the NASA Extreme Environment Mission Operations 10 (NEEMO 10) crew.

Before NOAA, Kohanowich served in the United States Navy for 23 years, retiring at the rank of Commander. Kohanowich later commented, "What really got me into diving was that the standards for women were the same [as for men]. Women had to do the same number of sit-ups and push-ups. They had to climb up and down the dive ladders wearing the same 200-pound Mark V dive system." Read more...

Recreational dive sites

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Flag of Chuuk.svg

Chuuk Lagoon, also previously known as Truk Lagoon, is a sheltered body of water in the central Pacific. About 1,800 kilometres (1,100 miles) north-east of New Guinea, it is located mid-ocean at 7 degrees North latitude, and is part of Chuuk State within the Federated States of Micronesia. The atoll consists of a protective reef, 225 kilometres (140 mi) around, enclosing a natural harbour 79 by 50 kilometres (49 by 31 miles), with an area of 2,130 square kilometres (820 square miles). It has a land area of 93.07 square kilometres (35.93 square miles), with a population of 36,158 people and a maximal height of 443 m. Weno city on Moen Island functions as the atoll's capital and also as the state capital and is the largest city in the FSM with its 13,700 people. Read more...

Underwater diving lists

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US Navy 091117-N-1291E-102 Navy Diver 2nd Class Ryan Arnold monitors the decompression chamber during a simulated medical emergency.jpg

Hyperbaric treatment schedules or hyperbaric treatment tables, are planned sequences of events in chronological order for hyperbaric pressure exposures specifying the pressure profile over time and the breathing gas to be used during specified periods, for medical treatment. Hyperbaric therapy is based on exposure to pressures greater than normal atmospheric pressure, and in many cases the use of breathing gases with oxygen content greater than that of air.

A large number of hyperbaric treatment schedules are intended primarily for treatment of underwater divers and hyperbaric workers who present symptoms of decompression illness during or after a dive or hyperbaric shift, but hyperbaric oxygen therapy may also be used for other conditions.

Most hyperbaric treatment is done in hyperbaric chambers where environmental hazards can be controlled, but occasionally treatment is done in the field by in-water recompression when a suitable chamber cannot be reached in time. The risks of in-water recompression include maintaining gas supplies for multiple divers and people able to care for a sick patient in the water for an extended period of time. Read more...

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In the News articles

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Photograph of the cramped interior of a cylinder containing two benches and two diver trainees

Diving disorders are medical conditions specifically arising from underwater diving. The signs and symptoms of these may present during a dive, on surfacing, or up to several hours after a dive. Divers have to breathe a gas which is at the same pressure as their surroundings (ambient pressure), which can be much greater than on the surface. The ambient pressure underwater increases by 1 standard atmosphere (100 kPa) for every 10 metres (33 ft) of depth.

The principal conditions are: decompression illness (which covers decompression sickness and arterial gas embolism); nitrogen narcosis; high pressure nervous syndrome; oxygen toxicity; and pulmonary barotrauma (burst lung). Although some of these may occur in other settings, they are of particular concern during diving activities.

The disorders are caused by breathing gas at the high pressures encountered at depth, and divers will often breathe a gas mixture different from air to mitigate these effects. Nitrox, which contains more oxygen and less nitrogen, is commonly used as a breathing gas to reduce the risk of decompression sickness at recreational depths (up to about 40 metres (130 ft)). Helium may be added to reduce the amount of nitrogen and oxygen in the gas mixture when diving deeper, to reduce the effects of narcosis and to avoid the risk of oxygen toxicity. This is complicated at depths beyond about 150 metres (500 ft), because a helium–oxygen mixture (heliox) then causes high pressure nervous syndrome. More exotic mixtures such as hydreliox, a hydrogen–helium–oxygen mixture, are used at extreme depths to counteract this. Read more...

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Every time I read, in a accident report, that the buddy system failed, I get livid. The buddy system does not fail, it is the people using it that have the problems. The system is fine, it is the implementation that falls down.Egstrom, G. H. (1992). "Emergency air sharing". Journal of the South Pacific Underwater Medicine Society. Retrieved 16 October 2016. </ref>

— Glen Egstrom, Emergency air sharing

Egstrom, G. H. (1992). "Emergency air sharing". Journal of the South Pacific Underwater Medicine Society. Retrieved 16 October 2016. 

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