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Underwater diving

Urheilusukeltajat ry dive club boat Räpylä, Finland

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.

 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.

Selected article

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

Diving medicine, also called undersea and hyperbaric medicine (UHB), is the diagnosis, treatment and prevention of conditions caused by humans entering the undersea environment. It includes the effects on the body of pressure on gases, the diagnosis and treatment of conditions caused by marine hazards and how relationships of a diver's fitness to dive affect a diver's safety.

Hyperbaric medicine is a corollary field associated with diving, since recompression in a hyperbaric chamber is used as a treatment for two of the most significant diving-related illnesses, decompression sickness and arterial gas embolism.

Diving medicine deals with medical research on issues of diving, the prevention of diving disorders, treatment of diving accidents and diving fitness. The field includes the effect of breathing gases and their contaminants under high pressure on the human body and the relationship between the state of physical and psychological health of the diver and safety.

In diving accidents it is common for multiple disorders to occur together and interact with each other, both causatively and as complications.

Diving medicine is a branch of occupational medicine and sports medicine, and an important part of diver education. Read more...

Selected equipment

Scuba 01.jpg

A diving regulator is a pressure regulator that reduces pressurized breathing gas to ambient pressure and delivers it to the diver. The gas may be air or one of a variety of specially blended breathing gases. The gas may be supplied from a scuba cylinder carried by the diver or via a hose from a compressor or high-pressure storage cylinders at the surface in surface-supplied diving. A gas pressure regulator has one or more valves in series which reduce pressure from the source, and use the downstream pressure as feedback to control the rate of flow and thereby the delivered pressure, lowering the pressure at each stage.

The terms "regulator" and "demand valve" are often used interchangeably, but a demand valve is a regulator that delivers gas only while the diver is inhaling and reduces the gas pressure to ambient. In single-hose regulators, the demand valve is the second stage, which is either held in the diver's mouth by a mouthpiece or attached to the full-face mask or helmet. In twin-hose regulators the demand valve is included in the body of the regulator which is usually attached directly to the cylinder valve or manifold outlet.

A pressure-reduction regulator is used to control the delivery pressure of the gas supplied to a free-flow helmet, in which the flow is continuous, to maintain the downstream pressure which is provided by the ambient pressure of the exhaust and the flow resistance of the delivery system (mainly the umbilical) and not influenced by the breathing of the diver. Gas-reclaim systems use a third kind of regulator to control the flow of exhaled gas to the return hose. Rebreather systems may also use regulators to control the flow of fresh gas, and demand valves, known as automatic diluent valves, to maintain the volume in the breathing loop during descent.

The performance of a regulator is measured by the cracking pressure and work of breathing, and the capacity to deliver breathing gas at peak inspiratory flow rate at high ambient pressures without excessive pressure drop. For some applications the capacity to deliver high flow rates at low ambient temperatures without jamming due to freezing is important. Read more...

Selected procedure

Junko-Kitahama Apnea-Monofin cropped.jpg

Freediving, free-diving, free diving, breath-hold diving, or skin diving is a form of underwater diving that relies on divers' ability to hold their breath until resurfacing rather than on the use of a breathing apparatus such as scuba gear.

Besides the limits of breath-hold, immersion in water and exposure to high ambient pressure also have physiological effects that limit the depths and duration possible in freediving.

Examples of freediving activities are: traditional fishing techniques, competitive and non-competitive freediving, competitive and non-competitive spearfishing and freediving photography, synchronized swimming, underwater football, underwater rugby, underwater hockey, underwater target shooting and snorkeling. There are also a range of "competitive apnea" disciplines; in which competitors attempt to attain great depths, times, or distances on a single breath.

Historically, the term free diving was also used to refer to scuba diving, due to the freedom of movement compared with surface supplied diving. Read more...

Selected biography

Craig B. Cooper is a professional aquanaut from the United States who served from 1991 to 2009 as Operations Manager for Aquarius, the world's only underwater habitat. Cooper is known to fellow divers by the nickname "Coop". Read more...

Selected wreck site

Regina ship in 1910.png

The SS Regina was a steel canaler built for the Merchant Mutual Line and home ported in Montreal, Quebec. Named after Regina, Saskatchewan, Regina had a tonnage of 1,956 gross register tons (GRT) and a crew of 32.

The ship sank during the Great Lakes Storm of 1913 after taking great damage. Lost for more than a half century, she became known as the "Great Mystery of the Great Storm of the Great Lakes". Since found, she has become an active dive site for scuba divers and is now part of Michigan's underwater Preserve system. Read more...

Selected dive site

Dos Ojos (from Spanish meaning "Two Eyes"; officially Sistema Dos Ojos) is part of a flooded cave system located north of Tulum, on the Caribbean coast of the Yucatán Peninsula, in the state of Quintana Roo, Mexico. The exploration of Dos Ojos began in 1987 and still continues. The surveyed extent of the cave system is 82 kilometers (51 mi) and there are 28 known sinkhole entrances, which are locally called cenotes. In January 2018, a connection was found between Sistema Dos Ojos and Sistema Sac Actun. The smaller Dos Ojos became a part of Sac Actun, making the Sistema Sac Actun the longest known underwater cave system in the world.

Dos Ojos lies north of the rest of the Sac Actun cave system. As a seprate system, Dos Ojos remained in the top ten, if not the top three, longest underwater cave systems in the world since the late 1980s. Dos Ojos contains the deepest known cave passage in Quintana Roo with 119.1 meters (391 ft) of depth located at "The Pit" discovered in 1996 by cave explorers who came all the way from the main entrance some 1,500 meters (4,900 ft) away. The deep passages include the "Wakulla Room", the "Beyond Main Base (BMB) passage", "Jill's room" and "The Next Generation passage". In August 2012 Dos Ojos was connected through a dry passage to Sistema Sac Actun. With March 2014 the total length of the combined system measures 319.05 kilometers (198.25 mi).

Dos Ojos is an anchialine cave system with connections to naturally intruding marine water and tidal influence in the cenotes. The coastal discharge point(s) of this cave system have not yet been humanly explored through to the ocean, although large volumes of groundwater were demonstrated by dye tracing to flow towards Caleta Xel-Ha, a nearby coastal bedrock lagoon.

The name Dos Ojos refers to two neighbouring cenotes that connect into a very large cavern zone shared between the two. These two cenotes appear like two large eyes into the underground. The original cave diving exploration of the whole cave system began through these cenotes. The Dos Ojos underwater cave system was featured in a 2002 IMAX film, Journey Into Amazing Caves, and the 2006 BBC/Discovery Channel series Planet Earth. Parts of the Hollywood 2005 movie The Cave were filmed in the Dos Ojos cave system.

Water temperature is 25 °C or 77 °F throughout the year, and the maximum depth near the Dos Ojos cenotes is approximately 10 meters (33 ft). The water is exceptionally clear as a result of rainwater filtered through limestone, and there being very little soil development in this region since the limestone is very pure. Read more...

Selected list

This is a list of notable military diving units and may contain combat units, salvage units, training units and diving research units which are present or past commands of any branch of the armed forces of any country.

  • Argentina: Tactical Divers Group (Buzos Tácticos) is the special operations unit of the Argentine navy. The operatives are combat divers, EOD/demolition technicians, and parachutists.
  • Austria: The Jagdkommando (German for Hunter force) is the Austrian Armed Forces' Special Operations group.
  • Australia:
    • Clearance Diving Branch is the Navy diving unit whose role covers all spheres of military diving,including Maritime counter terrorism-explosive ordnance disposal (MCT-EOD)
    • Army SAS is a dedicated special forces unit that undertakes water operations (emphasis of insertion onto land)
  • Bangladesh: 1st Para-commando Battalion of Bangladesh Army has frogman commando unit specialized for underwater demolition trained under supervision on Bangladeshi Naval special forces SWADS
  • Belgium: Special Forces Group (Belgium) has a specialized diving company for education and training of combat swimmers.
  • Brazil: Brazilian commando frogmen (GRUMEC) is a combat diver group
  • Canada: Canadian armed forces divers
  • Croatia: Croatian Special Operations Battalion (Croatia) (BSD)'s 3rd Company is specialized for seaborne operations and is responsible for training of combat swimmers and divers.
  • Denmark: Danish Frogman Corps (Danish: Frømandskorpset) is an elite special forces frogman corps in the Royal Danish Navy
  • Egypt: Combat frogmen: they played a major role on the War of attrition and the Crossing of the Suez Canal on 6 October 1973, by obstructing the oil pipes that would pump burning oil from Bar Lev Line to the canal.
  • Eritrea: During Eritrea's war of independence against Ethiopia, the rebel forces had a combat frogman force. After the war, some of those frogmen were retrained as dive guides for the sport scuba diving tourism trade.
Kultainen sukeltajamerkki.jpg

Selected image

Ice tube.jpg
Scientific diver passing through a hole in the polar ice

Categories

Underwater diving(33 C, 34 P)
Underwater divers(9 C, 21 P)
Underwater archaeology(4 C, 26 P)
Armed forces diving(1 C, 55 P)
Diving engineering(34 P)
Diving organizations(3 C, 47 P)
Diving equipment(16 C, 17 P, 2 F)
Underwater fiction(5 C, 2 P)
Free-diving(1 C, 31 P)
Underwater diving history(1 C, 7 P)
Manned submersibles(7 P)
Marine biology(8 C, 117 P, 1 F)
Marine salvage(1 C, 15 P)
Diving medicine(1 C, 62 P)
Underwater diving physiology(1 C, 11 P)
Underwater diving procedures(7 C, 35 P)
Professional diving(1 C, 4 P)
Recreational diving(2 C, 15 P)
Underwater diving safety(3 C, 34 P)
Scientific diving(2 C, 3 P)
Underwater security(1 C, 4 P)
Shipwreck law(1 C, 11 P)
Underwater diving sites(7 C, 15 P)
Sponge diving(1 C, 13 P)
Underwater diver training(1 C, 3 P)
Underwater sports(9 C, 31 P)

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