Scuba diving glossary, A to Z.

Definitions here describe what a term means and who uses it; they are not instructions. Skills, dive planning, gas handling and anything to do with an emergency are taught on a course by an instructor. Depth limits, ages and waiting times are each body's own published statement, with its date, not universal rules. Where sources disagree, each version is given. Park and wreck rules are summarised as of October 2026 and change, so check the managing authority's current text before you dive.

Jump to: A B C D E F G H I J L M N O P R S T U V W

A

Abandoned Shipwreck Act 1987

A US law under which the United States asserts title to abandoned shipwrecks embedded in a state's submerged lands or in its protected coral formations, or lying on state submerged lands and listed on or eligible for the National Register, and passes that title to the state. It also directed the National Park Service to publish guidelines that include access for recreational divers and partnerships with sport divers. (US wreck law)

Adjustable buoyancy life jacket (ABLJ)

An early buoyancy device. Wikipedia (secondary) says Maurice Fenzy of the French firm Fenzy invented it in 1961, that the firm's name became a byword for the item, and that such jackets became available during the 1960s. Today's European BCD standard, EN 1809, excludes life preservers and personal flotation devices from its scope. (The buoyancy jacket)

Adventure Dive

A single introductory dive in a specialty area, used to build an advanced course. PADI's Advanced Open Water Diver is made of five Adventure Dives, SSI's Advanced Adventurer requires at least five different ones, and SDI says one dive from each Advanced Adventure specialty may be credited toward that full specialty. (Specialty certifications)

Advanced Open Water Diver

PADI's second recreational level. PADI's blog (updated August 2024) says it certifies to 30 m (100 ft) with a minimum age of 12, or 10 for Junior Advanced Open Water, and PADI's 2024 restrictions article limits ages 12 to 14 to 21 m. Other agencies publish their own next steps, such as BSAC's Advanced Ocean Diver, which BSAC's undated course page says permits dives to 30 m without decompression stops. (Certification levels)

Air integration

Showing cylinder pressure on the dive computer. PADI describes hoseless air integration as a transmitter on the regulator's first stage sending the pressure wirelessly to the computer, and lists air integration as an optional computer feature. (Dive computers)

Alpha flag

The blue-and-white International Code Flag A. A Washington State boater-education guide says a vessel restricted in its ability to manoeuvre by diving must show a rigid one at least one metre high, visible all round. See also divers-down flag. (Lights and signalling)

Ambient pressure

The pressure of the surrounding water at the diver's depth. DAN describes a regulator as delivering gas at ambient pressure. PADI says pressure rises by 1 ATA (one atmosphere absolute) for every 10 m (33 ft) of descent in sea water, and SSI gives roughly one extra atmosphere per 10 m. (Dive physics explained)

Aqua-Lung

The open-circuit breathing set developed by Jacques-Yves Cousteau and the engineer Emile Gagnan in 1943. Wikipedia (secondary) calls the twin-hose design the first successful and safe open-circuit scuba, and says the first production model was sold in France as the CG45. Sources disagree on when the two men began working together (1942 or 1937) and on the patent dates. (The Aqua-Lung)

Archimedes' principle

As PADI states it, an object in water is pushed up by a force equal to the weight of the water it displaces. PADI presents it with Boyle's law as the basis of buoyancy. (Dive physics explained)

Arterial gas embolism (AGE)

One of the two forms of decompression illness. DAN describes it as gas entering the arterial circulation, typically after lung tissue is injured by expanding air during ascent, calls it the more serious form and says it can be fatal. Denoble and colleagues (2008) recorded it as the disabling injury in 29 percent of the deaths they could classify. It needs prompt medical care from a doctor. (Decompression sickness and barotrauma)

Autonomous diver

Level 2 of ISO 24801 (ISO 24801-2:2014), the competency level at which a training organisation may issue a qualification for diving without a dive professional. Wikipedia (secondary) maps entry-level cards such as PADI and SSI Open Water Diver, CMAS One Star and BSAC Ocean Diver to it, and gives EN 14153-2 as the European equivalent. (ISO diver standards)

B

Back-inflate BCD

A buoyancy compensator whose bladder sits only behind the diver. SSI says it gives a streamlined, horizontal position in the water. (BCDs)

Backplate and wing

A modular buoyancy system. Wikipedia (secondary) describes a rigid plate, usually stainless steel or anodised aluminium, on a webbing harness, with a separate inflatable wing between plate and cylinder. SSI says wings offer high lift and are popular with technical divers and those carrying extra cylinders. (BCDs)

Balanced regulator

DAN's Alert Diver (2012) says an unbalanced first stage's intermediate pressure can drift as the cylinder empties or the depth changes, which can make breathing harder, while a balanced first stage uses a balance chamber to keep it steadier. A balanced second stage reduces the cracking effort needed to start each breath. (Regulators)

BCD (buoyancy compensator)

The inflatable jacket or wing that, as PADI puts it, lets a diver float at the surface, rest on the bottom or hover mid-water, and that holds the cylinder. PADI lists its essential parts as a low-pressure inflator with oral inflation, a deflator and an overpressure relief valve. The European standard is EN 1809:2014+A1:2016. (BCDs)

Bends

The popular name for decompression sickness, as DAN notes. See decompression sickness. (Decompression sickness and barotrauma)

Blue Star

The Florida Keys National Marine Sanctuary's recognition programme for operators committed to responsible diving and snorkelling. NOAA encourages visitors to book with a Blue Star operator; this site does not name operators. (Florida Keys)

Boyle's law

As PADI states it, for a fixed amount of gas at constant temperature, pressure and volume are inversely proportional: as one goes up, the other goes down. PADI presents it, with Archimedes' principle, as the basis of buoyancy. (Dive physics explained)

BSAC (British Sub-Aqua Club)

The UK club-based training body, founded by Oscar Gugen and Peter Small at the Waldorf Hotel, London, on 15 October 1953. BSAC says it was a founding member of CMAS in 1959, approved nitrox for members in 1995 and rebreathers in 2001. Its sources disagree on how many attended the first meeting (100, or 22 who formed the first branch). (Training agencies)

Bubblemaker

PADI's children's pool experience. PADI's 2024 restrictions article gives a minimum age of 8 and a depth of 2 m (6 ft); it is not a certification. (Try diving)

Buddy system

Diving in pairs, or sometimes threes, as a set of safety practices; that is how Wikipedia (secondary) defines buddy diving. PADI (2022) says diving with a buddy is safer than diving solo, giving a nearby backup air source and someone who can help, and DAN Europe (2012) treats buddy separation as a significant weak point. (Buddy and solo diving)

Buhlmann ZHL-16C

A decompression model from the Swiss physician Albert A. Buhlmann. Wikipedia (secondary) says his research, begun in 1959, was published in book form in 1983, and that ZH-L16 stands for Zurich, limits and 16 compartments. Suunto describes it as a dissolved-gas model with 16 theoretical tissue groups (maker statement). (The first dive computers)

C

C-card (certification card)

The card that shows a diver completed an agency's course. Wikipedia (secondary) says it typically shows the agency, the holder's name and photo, the certification type and date and the instructor, and that dive shops, boats and resorts may ask for it before filling cylinders, renting gear or allowing a dive. PADI says it produced the first photo certification card in 1968 (agency claim). (Why certification matters)

Carbon dioxide retention

A build-up of carbon dioxide in the body. DAN's Alert Diver (Simon Mitchell, 2016) says divers are predisposed to it through work of breathing, reduced breathing drive, skip breathing and equipment dead space, that effects include breathlessness, headache and unconsciousness, and that it can worsen narcosis, oxygen toxicity and decompression illness. It needs prompt medical care from a doctor. (Other diving illnesses)

Carbon monoxide

An odourless, colourless poisonous gas from incomplete combustion. DAN's Travelers Medical Guide says it can get into scuba cylinders that are carelessly filled, and can also come from boat exhaust in poorly ventilated spaces. Carbon monoxide poisoning needs prompt medical care from a doctor. (Other diving illnesses)

Cardiac events

Heart problems while diving. DAN's cardiovascular fitness page says they cause 20 to 30 percent of diving deaths, while Denoble and colleagues (2008) recorded cardiac incidents as 26 percent of disabling injuries and 13 percent of recorded causes of death; the figures measure different things. The 2008 study linked them to existing heart disease and age over 40. A cardiac event needs prompt medical care from a doctor. (Fitness to dive)

Cave Diving Group (CDG)

A UK cave diving club formed in 1946, which describes itself as the oldest amateur technical and cave diving organisation in the world. Wikipedia (secondary) names Graham Balcombe as founder; the CDG's own page calls him a co-founder. (Cave and technical diving)

Cavern diving

Diving in the entrance area of a cave. TDI says its Cavern Diver course covers cavern (overhead) environments and is not intended for cave diving. The NSS Cave Diving Section calls its cavern course a safety and awareness course that does not count toward cave certification, and stresses staying within sight of the entrance and daylight. (Specialty certifications)

CDWS (Chamber of Diving and Watersports)

Egypt's dive-industry body, created on 17 April 2007 under the Ministry of Tourism. Its 2009 depth-limitation policy (version 6) required dive operations to comply with ISO 24803:2007 / EN 14467:2004 to be licensed and set 40 m as the maximum on compressed air where training allows; the policy may since have been superseded. (Red Sea parks)

CE marking

The European conformity mark on equipment such as regulators. DAN Europe (2022) stresses that it confirms only that minimum requirements were met, that real performance varies with design, temperature and depth, and that non-original parts may void it. (Regulators)

Charles' law

The link between a gas's temperature and its pressure. PADI illustrates it with a cylinder cooling in the water. (Dive physics explained)

CMAS

The Confederation Mondiale des Activites Subaquatiques (World Underwater Federation), set up in Monaco on 9 to 11 January 1959 with Jacques-Yves Cousteau as first president, per Wikipedia (secondary). It certifies by star grades: One Star, Two Star and Three Star. Wikipedia gives two different counts of its members in the same article. (Training agencies)

Cold shock

DAN's Travelers Medical Guide says sudden immersion in water below about 15 C without thermal protection can trigger a dangerous cold-shock response, including a gasp reflex that can lead to inhaling water. (Environmental hazards)

Confined water

A pool or sheltered water used in training before open water dives. PADI's 2018 blog gives five confined water sessions for Open Water Diver, and GUE's Open Water Diver lists at least ten. (Getting started)

Controlled Site

A military wreck designated under the UK's Protection of Military Remains Act 1986 that may be dived only under a Ministry of Defence licence, according to the Royal Navy's 2026 question-and-answer document for BSAC. Compare Protected Place. (UK protected wrecks)

Cracking effort

The effort a diver needs to start the flow of gas from a second stage. DAN (2012) says balanced second stages reduce it, and many second stages have a knob that adjusts breathing resistance. (Regulators)

CSA B339

The Canadian standard that, according to Transport Canada, governs periodic requalification of cylinders and is adopted by reference in the Transportation of Dangerous Goods Regulations. Transport Canada says a cylinder may be filled only within its requalification period. (Cylinder inspection and testing)

Current

Moving water. DAN's Alert Diver (Mike Ange, 2010) calls currents one of the most underestimated and physically demanding conditions a diver can meet, says that because water is far denser than air even a moderate current creates great resistance, and advises training before diving in strong current. (Environmental hazards)

D

DAN (Divers Alert Network)

A diving safety organisation. DAN runs a fatality surveillance programme, joined in 1989 the data collection that John McAniff began at the University of Rhode Island in 1970, publishes the Annual Diving Report, and keeps a Recompression Chamber Network. DAN Europe is a separate organisation. (What the accident data shows)

DAN Annual Diving Report

DAN's yearly analysis of incidents and deaths. The 2020 edition, released in November 2022, covers 2018; DAN Europe's summary of it reports 189 diving-related deaths worldwide that year, 100 of them in recreational and technical scuba. A newer edition could not be confirmed in our research. (What the accident data shows)

Dalton's law

As PADI states it, the total pressure of a gas mixture equals the sum of the partial pressures of the gases in it. (Dive physics explained)

Decompression illness (DCI)

DAN's umbrella term for two conditions linked to reduced surrounding pressure: decompression sickness and arterial gas embolism. DAN says suspected DCI needs prompt medical evaluation and is treated in a hyperbaric (recompression) chamber. It needs prompt medical care from a doctor. (Decompression sickness and barotrauma)

Decompression sickness (DCS)

Also called the bends. DAN describes it as bubbles forming in body tissues when pressure falls too quickly for dissolved nitrogen or other inert gas to leave the body in an orderly way, and says it can occur even when accepted guidelines have been followed. It needs prompt medical care from a doctor. (Decompression sickness and barotrauma)

Deep Diver

A specialty certification for dives beyond entry-level depths. PADI's blog (updated August 2024) says its Deep Diver certifies to 40 m (130 ft) with a minimum age of 15. On undated pages, SSI says its Deep Diving covers 18 to 40 m, NAUI says its course covers no-stop dives between 18 and 40 m, and SDI says its course certifies to a maximum of 40 m. (Depth limits by certification)

Delayed surface marker buoy (DSMB)

PADI describes it as an inflatable signal tube attached to a line and reel that can be deployed from underwater or at the surface. DAN says it can mark a diver before surfacing but needs training, because handling the line while inflating is tricky. (Lights and signalling)

Demand regulator

A regulator that delivers gas only when the diver inhales; DAN says scuba regulators are demand-type. The Blutime Scuba History site says Benoit Rouquayrol patented a self-breathing apparatus in April 1860, the root of the later Rouquayrol-Denayrouze apparatus. (Before the Aqua-Lung)

DIN and yoke

Two ways a regulator's first stage connects to a cylinder valve. Mares' REBEL manual lists its first stages with a DIN 477/50 screw fitting rated to 300 bar or an international yoke (CGA 850) rated to 232 bar (maker statement). (Regulators)

Disabling injury

One step in the causal analysis used by Denoble and colleagues (2008) on 947 recreational scuba deaths: trigger, disabling agent, disabling injury and cause of death. The most frequent disabling injuries were asphyxia (33 percent), arterial gas embolism (29 percent) and cardiac incidents (26 percent), and the authors judged the disabling injury more informative than the recorded cause of death. (What the accident data shows)

Discover Scuba Diving

PADI's try-dive programme. PADI's 2024 restrictions article gives a minimum age of 10 and a depth of 12 m (40 ft), and Wikipedia (secondary) says it can count toward Open Water Diver if done within a year. It is not a certification. (Try diving)

Dive computer

A wrist or console instrument that, as PADI describes it, combines depth and time with a decompression model to estimate nitrogen uptake and show remaining no-stop time. PADI quotes DAN that algorithms give guidance, not guarantees. (Dive computers)

Dive Leader

Level 3 of ISO 24801 (ISO 24801-3:2014), the dive leadership level. BSAC also uses Dive Leader as a grade name, and Iceland's 2013 Silfra instructions require guides to be trained to the Dive Leader level (EN 14153-3 / ISO 24801-3). (ISO diver standards)

Divemaster

PADI's first professional level. PADI's blog (2025) lists prerequisites including age 18, Rescue Diver, 40 logged dives to start and 60 to certify, and physician clearance within 12 months. SSI also calls Divemaster its first professional step. (Certification levels)

Diver Medical Participant Questionnaire

The diver's form in the 2020 Recreational Diving Medical Screening System, published in June 2020 by the international Diver Medical Screen Committee and endorsed by the WRSTC on 9 June 2020. As PADI describes it, a yes on the first page leads to more specific questions, and a yes there means a physician must approve diving. It never tells anyone whether they are fit to dive; a physician decides. (Medical screening)

Divers-down flag

The red flag with a white diagonal stripe. Sources disagree on its legal status in the US: a Washington State guide says it does not meet state and federal display requirements, while other sources say it is required by state law or regulation almost everywhere. The Florida Keys sanctuary rule, 15 CFR 922.163(a)(6), requires divers to show either it or the alpha flag in federal waters. (Lights and signalling)

DOT 3AL and 3AA

US Department of Transportation specifications for aluminium (3AL) and steel (3AA) cylinders. Under 49 CFR 180.209, 3AL cylinders are requalified every 5 years; 3AA cylinders have 5, 10 or 12-year periods depending on conditions, and the 10-year option excludes cylinders used for underwater breathing. (Cylinder inspection and testing)

Drowning

DAN's Travelers Medical Guide defines it as breathing impairment from being submerged. Denoble and colleagues (2008) recorded it as the cause of death in 70 percent of the recreational scuba deaths they studied, but found it was often secondary to an injury that had already disabled the diver. It needs prompt medical care from a doctor. (What the accident data shows)

Dry suit

A suit that seals at the wrists and neck to keep water out, as PADI describes it. DAN (2012) names shell or membrane suits, which rely on undergarments for warmth, and foam neoprene suits, which insulate themselves, and says dry-suit diving needs training and practice. (Dry suits)

E

Eddy current examination

A test for cracks in cylinder necks. 49 CFR 180.209(m) requires DOT-3AL cylinders made of 6351-T6 aluminium in scuba service to have one every 5 years with a visual inspection, on top of normal requalification; Luxfer, a cylinder maker, requires one at least every 2.5 years for its 6351 cylinders in an undated FAQ (maker statement). (Cylinder inspection and testing)

EN 250

The European standard for open-circuit compressed-air scuba, current edition EN 250:2014, aiming at minimum safe operation to 50 m. DAN Europe (2022) says an EN250 regulator was tested to 50 m and in water as cold as 4 C, that "EN250 >10 C" means approved only for water above 10 C, and that the letter A marks a first stage tested for two divers at once. (Regulators)

EN 1809

The European standard for buoyancy compensators, EN 1809:2014+A1:2016. Its scope covers inflatable buoyancy-control devices that may carry the breathing set or weights, and excludes life preservers, personal flotation devices and rescue devices. (BCDs)

EN 13319

The European standard for depth gauges and combined depth-and-time devices, EN 13319:2000. Its scope expressly excludes any information other than depth and time, so a dive computer's decompression information is not covered by it. (Dive computers)

EN 13949

The European standard EN 13949:2003 for open-circuit scuba used with nitrox containing more than 22 percent oxygen, or with oxygen; it adds requirements and tests on top of EN 250. (Nitrox equipment)

EN 16805, EN 1972 and EN 16804

The European standards for diving masks (EN 16805:2015, excluding full-face masks), snorkels (EN 1972:2015, excluding combined mask-and-snorkel units) and open-heel fins (EN 16804:2015). Our research found no CEN standard for full-foot fins, and the current status of EN 16805 could not be confirmed. (Masks, snorkels and fins)

Enriched air nitrox (EAN)

A nitrogen and oxygen breathing mix richer in oxygen than air; the European equipment standard EN 13949 covers nitrox above 22 percent oxygen. X-Ray Magazine (2023) says a 1988 NOAA and Harbor Branch workshop proposed the name "Enriched Air Nitrox"; NAUI says it was the first recreational agency to adopt NOAA's nitrox standards, in 1992 (agency claim). SSI's standard, seen only in a search summary, certifies at two levels, EAN32 and EAN40. Wikipedia (secondary) says the US RSTC publishes a separate minimum standard for nitrox certification, and BSAC includes basic nitrox training in its Ocean Diver course. (Nitrox comes to recreational diving)

Equalisation

Balancing the pressure in an air space, such as the middle ear or a mask, with the surrounding water pressure. PADI says a scuba mask must enclose the nose because its airspace has to be equalised on descent, and DAN names poor equalisation technique as a contributor to ear injury. How to equalise is taught by an instructor. (Decompression sickness and barotrauma)

Equivalent air depth (EAD)

A nitrox concept named here only as history. NAUI credits Dr J. Morgan Wells with developing the EAD formula in 1970 and says NOAA's Nitrox I standards of 1978 were developed from that work. (Nitrox comes to recreational diving)

F

Fernez-Le Prieur apparatus

A self-contained compressed-air set shown at the Tourelles pool in Paris on 6 August 1926, combining Maurice Fernez's breathing device with a portable cylinder added by Yves Le Prieur. Wikipedia (secondary) calls it the first open-circuit scuba but a manually adjusted free-flow system with low endurance; sources differ on how much credit Fernez is due. (Before the Aqua-Lung)

Fins: full-foot and open-heel

PADI (2019) describes full-foot fins as worn barefoot, light and suited to warm water, and open-heel fins as worn over boots, more powerful with heavy gear and warmer. It names paddle, channel, split and hinged blade designs. (Masks, snorkels and fins)

First stage

The part of a regulator fixed to the cylinder valve. DAN says it reduces cylinder pressure to an intermediate pressure, and comes in piston and diaphragm types. (Regulators)

Florida Keys National Marine Sanctuary

A US marine sanctuary that NOAA says was designated on 16 November 1990 after a series of boat groundings; Wikipedia (secondary) gives 28 December 1990. Florida's DEP says it is managed jointly by NOAA and two Florida agencies, and its rules are in 15 CFR part 922 subpart P. (Florida Keys)

Flying after diving

Waiting before a flight after diving. DAN's 2002 workshop consensus suggests at least 12 hours after a single no-decompression dive and 18 hours after multiple dives per day or multiple days, while PADI's blog (updated 2024) recommends 24 hours after any diving. These are each body's published figures, not rules, and DAN says they reduce but do not guarantee avoiding decompression sickness. (Flying after diving)

G

Galapagos National Park Directorate (DPNG)

The authority that manages both the Galapagos National Park and the Galapagos Marine Reserve. Its visit-rules resolution MAE-PNG/DIR-2026-0044-RM, signed on 12 August 2026 and published on 14 September 2026, requires an accredited naturalist guide and sets minimum distances from wildlife. (Galapagos)

Gradient factors

Settings that adjust how conservative a Buhlmann-based decompression model is. Suunto says its Buhlmann 16 GF model sets conservatism by gradient factors and flags non-default values as outside its recommendation (maker statement). (Dive computers)

Green Fins

A reef-protection programme for dive and snorkel operators. Wikipedia (secondary) says it was set up in 2004 as a United Nations Environment Programme initiative, is now led by the UK charity The Reef-World Foundation, and has a 15-point code of conduct that member operators pledge to follow. (Protecting reefs and marine life)

GUE (Global Underwater Explorers)

A not-for-profit training organisation formed by Jarrod Jablonski and launched on 1 July 1998 with seven cave, technical and rebreather courses, per GUE's own magazine. Wikipedia (secondary) associates it with the "Doing It Right" approach and Hogarthian equipment configuration. (Training agencies)

H

Halley's diving bell

Edmond Halley's diving bell design, reported to the Royal Society in late 1691; the Society holds a sketch dated 30 September 1691. Its own record disagrees on who drew it. (Before the Aqua-Lung)

Helium mixes

Breathing gases that contain helium, such as trimix and heliox. DAN's Alert Diver (2017) says helium is not narcotic, so it is used in mixes for deeper dives, and that very deep helium dives can cause high-pressure nervous syndrome. BSAC says it sanctioned trimix for members, with depth limits, in 2001. (Cave and technical diving)

Henry's law

As PADI states it, the amount of gas dissolved in a liquid is proportional to the pressure outside the liquid. DAN's medical reference describes body tissues taking up inert gas under pressure, the process decompression models try to estimate. (Dive physics explained)

HEPCA

The Hurghada Environmental Protection and Conservation Association, an Egyptian NGO founded in 1992 and registered in 1995. It runs a mooring-buoy network that it reports at about 1,400 buoys, which it traces to a 1988 meeting about anchor damage. (Red Sea parks)

High-pressure nervous syndrome

A condition DAN's Alert Diver (2017) says very deep dives on helium mixes can cause. Wikipedia (secondary) gives it as the probable cause of Sheck Exley's death at Zacaton in 1994. (Other diving illnesses)

Historic Marine Protected Area

Scotland's designation for historic marine sites under the Marine (Scotland) Act 2010, which replaced the Protection of Wrecks Act there. Divernet reports that removing, altering or disturbing a protected site has been a criminal offence since the first were designated in 2013, and that Scapa Flow and the Queen of Sweden were designated from 1 November 2025. (UK protected wrecks)

Hydrostatic test (requalification)

A pressure test used to requalify a cylinder. In the US, 49 CFR 180.209 sets 5-year requalification for scuba cylinders; BSAC, relaying the UK test body IDEST in 2020, gives a full inspection and hydraulic test every five years for UK recreational cylinders; France's FFESSM (2017) gives 2 years, or 6 with yearly TIV inspection. Your test station and local rules decide. (Cylinder test date checker)

Hypothermia

DAN's Travelers Medical Guide defines it as a core temperature below 35 C and says water draws heat from the body far faster than air; even warm tropical water can cool a person slowly without protection. DAN also notes divers can overheat on land, especially in dry suits. Hypothermia and overheating both need prompt medical care from a doctor. (Environmental hazards)

I

IANTD

The International Association of Nitrox and Technical Divers. Wikipedia (secondary) says it began as the International Association of Nitrox Divers (IAND), formed in 1985 by Dick Rutkowski to teach nitrox to recreational divers; most sources date the change of name to 1992, one to 1991. (Nitrox comes to recreational diving)

Immersion pulmonary oedema (IPE or IPO)

Fluid building up in the lungs of divers and swimmers. DAN links it to upright immersion shifting blood into the chest, lists cold water, exertion and denser breathing gas among contributors, and says repeat episodes are likely. BSAC's 2024 incident report recorded seven confirmed cases. It needs prompt medical care from a doctor. (Other diving illnesses)

Instructor Development Course (IDC)

PADI's instructor course. PADI's blog (2024) lists prerequisites of age 18, certified for at least six months, Divemaster or equivalent and 60 logged dives to start, with 100 to certify as an instructor. (Certification levels)

Intermediate pressure

The pressure in the hose between a regulator's first and second stages. DAN (2012) gives it as typically about 125 to 145 psi above ambient. (Regulators)

Introductory diving

A try dive. Wikipedia (secondary) describes it as a dive with no prior training under an instructor's guidance that issues no certification. ISO 11121:2017 sets minimum content for introductory programmes that go into open water. (Try diving)

Irukandji syndrome

A reaction to stings from certain box jellyfish. DAN's Alert Diver (2021) says symptoms usually start 5 to 90 minutes after the sting and that about 3 percent of cases progress to heart failure. It needs emergency medical care. (Environmental hazards)

ISO 11121

ISO 11121:2017, the requirements for introductory programmes to scuba diving that take participants into open water. It is not a qualification standard. (ISO diver standards)

ISO 18119

The international standard for periodic inspection and testing of seamless steel and aluminium gas cylinders. BSAC says BS EN ISO 18119:2018, published October 2018, replaced the earlier UK standards BS EN 1968:2002 and BS EN 1802:2002. (Cylinder inspection and testing)

ISO 24801

"Recreational diving services: Requirements for the training of recreational scuba divers", in three parts: Level 1 Supervised diver, Level 2 Autonomous diver and Level 3 Dive leader. All three current parts are 2014 editions that replaced 2007 ones. (ISO diver standards)

ISO 24803

ISO 24803:2017, the requirements for recreational diving providers. It covers five service types: introductory diving, snorkelling excursions, training, organised and guided diving for qualified divers, and equipment rental. (ISO diver standards)

J

Jacket BCD

The style PADI calls the most popular for recreational diving: harness and bladder in one unit, with the bladder wrapping forward under the arms. SSI says it inflates front, back and sides and holds the diver upright at the surface. (BCDs)

Joule-Thomson effect

The cooling of a gas as its pressure drops, which PADI illustrates with gas passing through the regulator. (Dive physics explained)

Junior Open Water Diver

The entry-level card for younger divers. PADI certifies ages 10 to 14 as Junior Open Water Divers, with 12 m for ages 10 to 11 and 18 m for ages 12 to 14 under its 2024 restrictions, and converts them automatically at 15. SSI's Open Water Diver standard (archived October 2025) also certifies under-15s as Junior Open Water Divers. (Certification levels)

L

LARU (Lambertsen Amphibious Respiratory Unit)

Christian J. Lambertsen's oxygen rebreather. The National Academy of Engineering's 2012 memorial tribute says he presented it to the Office of Strategic Services as a medical student, first as the Lambertsen Lung. Wikipedia (secondary) notes that the word SCUBA was first applied to his rebreather, not to the Aqua-Lung. (Lambertsen and the word scuba)

Lift capacity

The weight a BCD can hold up at the surface, as SSI defines it. SSI says cold-water divers in thick suits and technical divers with several cylinders need more than warm-water divers. (BCDs)

Logbook

A diver's record of dives. Wikipedia (secondary) separates it from the C-card: the card records training, the logbook is evidence of the range of a diver's experience. Agencies use logged dives as course prerequisites. (Why certification matters)

M

Marine National Park Zone

One of eight zones in the Great Barrier Reef Marine Park Zoning Plan 2003, meant to protect natural integrity generally free from extractive activity. The plan allows low-impact activities that take nothing, plus photography and filming, without permission; running a tourist programme there needs the Authority's permission. (Great Barrier Reef)

Mask volume

The air space inside a mask. PADI says low-volume masks sit closer to the face and clear more quickly, while high-volume masks feel more open and widen peripheral vision but take more effort to clear. (Masks, snorkels and fins)

Maximum operating depth (MOD)

A depth figure tied to a particular nitrox mix. SDI (2012) says a nitrox cylinder's tag or label must show it alongside the exact oxygen fraction. How it is worked out is taught in nitrox training. (Nitrox equipment)

Middle-ear barotrauma

Ear squeeze. DAN calls it the most common dive injury and describes it as injury from unequalised pressure in the middle ear, which can cause swelling, bleeding and a ruptured eardrum. DAN advises a medical evaluation for a suspected case. It needs prompt medical care from a doctor. (Decompression sickness and barotrauma)

Mooring buoy

A fixed buoy boats tie to instead of anchoring on reef. STINAPA sets time and size limits on Bonaire's public moorings, HEPCA runs a network in the Egyptian Red Sea, and the Florida Keys sanctuary rule 922.163(a)(8) bans tampering with mooring buoys. (How dive sites are protected)

Mousquemers

The nickname naval officer Philippe Tailliez coined for himself, Jacques-Yves Cousteau and free-diver Frederic Dumas, after The Three Musketeers, per Wikipedia (secondary). National Geographic says the three made more than 500 dives with the Aqua-Lung in 1943. (The Aqua-Lung)

N

NAUI

The National Association of Underwater Instructors. NAUI's heritage page says the National Diving Patrol was renamed NAUI in 1959 and that its first major instructor course, in Houston in 1960, certified 72 candidates; a NAUI release seen in search results says 53 graduated, and sources differ on whether 1959 or 1960 is the founding year. (Training agencies)

Natural protectorate (Egypt)

A protected area declared by Prime Minister's decree under Law No. 102 of 1983. The Egyptian Environmental Affairs Agency's July 2026 table lists Ras Mohammad, declared in 1983, first; HEPCA's page gives the law's year as 1982. (Red Sea parks)

Nitrogen narcosis

DAN's Alert Diver (2017) says nitrogen's narcotic effect typically begins around 24 to 30 m on air or nitrox, and that it varies between people and from dive to dive; DAN (2021) describes impaired judgment and mood swings. Wikipedia (secondary) says Frederic Dumas was the first scuba diver to report it, in October 1943. (Other diving illnesses)

NOAA Nitrox I

The nitrox standard NOAA approved agency-wide in 1978, per X-Ray Magazine (2023), with its tables appearing in the NOAA Diving Manual in 1979. Sources date Morgan Wells's start on nitrox at NOAA to 1970 or 1977. (Nitrox comes to recreational diving)

No-stop time

The time a dive computer's model estimates is left before a dive would need decompression stops. PADI lists remaining no-stop time as a standard computer display; it is an estimate, not a guarantee. (Dive computers)

NSS Cave Diving Section (NSS-CDS)

The cave diving section of the US National Speleological Society, founded in 1973 with Sheck Exley as first chairman (Wikipedia gives 6 February 1974 for his start). It says it was the world's largest cave diving organisation by 1976, and it published Exley's "Basic Cave Diving: A Blueprint for Survival" in 1979. (Cave and technical diving)

O

Ocean Diver

BSAC's entry-level open water qualification. BSAC's undated course page gives a maximum depth of 20 m and a minimum age of 12. BSAC says Ocean Divers may dive together under a Dive Manager's supervision only at familiar sites and in conditions met in training. (Certification levels)

Octopus

The common name for a spare second stage carried as an alternate air source. Quebec's terminology office traces the name to the look of a diver's many hoses. Wikipedia (secondary) notes it runs from the diver's own supply, so it is not a redundant gas source for that diver, and credits Sheck Exley with helping standardise it in cave diving. (Regulators)

Ohgushi Peerless Respirator

A Japanese breathing apparatus first patented in Japan in 1918, according to a 2016 UW360 article, which credits Watanabe Riichi, Ohgushi Kanezo and Captain Kataoka Kyuhachi. Wikipedia (secondary) gives the machinist's name as Iwao Ogushi in recent Japanese sources. (Before the Aqua-Lung)

Open circuit

Scuba in which exhaled gas goes into the water. Wikipedia (secondary) describes it as one or more high-pressure cylinders delivering gas at ambient pressure through a regulator, as opposed to a rebreather. (How scuba diving works)

Open Water Diver

The entry-level certification at PADI, SSI and others. PADI's blog (2018) says it lets a diver dive with a certified buddy to 18 m (60 ft), the figure PADI's 2024 restrictions article also gives, and PADI says it launched the course in 1972. SSI, in an undated article, gives the same 18 m figure; BSAC's undated course page gives 20 m for its entry level, Ocean Diver. (Certification levels)

Orca EDGE

The Electronic Dive Guide, launched by Orca Industries in January 1983. A Shearwater blog (2017) calls it the first commercially viable microprocessor-based dive computer (a maker's blog, so a claim); sources disagree on whether the EDGE or the Hans Hass DecoBrain came first and on the EDGE's year. (The first dive computers)

Overhead environment

The term used for caves, caverns and wrecks as dive environments; TDI describes caverns as overhead environments. The NSS Cave Diving Section's cavern course stresses staying within sight of the entrance and daylight, and Iceland's Silfra rules ban diving into caves, passages and tunnels. (Diving within your training)

Overpressure relief valve

One of the three essential parts of a BCD in PADI's list, alongside the inflator and the deflator. (BCDs)

Oxygen service

Equipment cleaned and kept for use with oxygen-rich gas. The bodies set different thresholds: 22 percent in EN 13949's scope, 23.5 percent in DAN's equipment page and for Luxfer cylinders, 25 percent in DAN's 2022 article, and 40 percent in SDI's 2012 guidance. DAN (2022) says only trained, competent technicians should perform oxygen cleaning. (Nitrox equipment)

Oxygen toxicity

DAN's Alert Diver (2017) says high oxygen partial pressures can cause central nervous system oxygen toxicity, with seizures that may lead to drowning, that it can happen at recreational depths without warning, and that risk rises with exposure time, exertion and some medicines. It needs prompt medical care from a doctor. (Other diving illnesses)

P

PADI

The Professional Association of Diving Instructors, founded in 1966 in Illinois by John Cronin and Ralph Erickson. On its 60th-anniversary history page (2026) PADI claims over 30 million certified divers; its own counts differ between certifications and divers (agency claims). (Training agencies)

Patent foramen ovale (PFO)

A hole in the wall between the heart's upper chambers, as DAN describes it. DDRC Healthcare says about 20 to 25 percent of people have one and that it usually causes no problems in daily life; it advises divers who think they may have one to see a cardiologist with an interest in diving. (Other diving illnesses)

Personal locator beacon

A satellite SOS device; DAN says some can send messages and their batteries need regular checking. (Lights and signalling)

Project AWARE

The Project AWARE Foundation, a diver conservation group. PADI's professional blog announced that it published "10 Tips for Divers to Protect the Ocean Planet" in January 2014, which Scubaverse describes as a code of conduct beginning "be a buoyancy expert" and including "take only photos, leave only bubbles". (Protecting reefs and marine life)

Protected Place

A military wreck designated under the UK's Protection of Military Remains Act 1986 that may be dived, but whose enclosed interior must not be entered and from which nothing may be removed; GOV.UK calls it "look but don't touch". A 2026 Armed Forces Bill clause would make every wreck lost in military service a Protected Place; it is proposed, not yet law. (UK protected wrecks)

Protection of Wrecks Act 1973

The UK law, in force from 18 July 1973, that lets the government designate a restricted area around a historic wreck, where diving directed at the wreck or disturbing it needs a licence, and a prohibited area around a dangerous wreck. It no longer applies to historic wrecks in Scotland. (UK protected wrecks)

Pulmonary barotrauma

Lung over-expansion injury. DAN's Alert Diver (Nicholas Bird, MD, 2013) describes a chain in which running out of gas, entrapment or equipment trouble leads to a rapid ascent, lung over-expansion and arterial gas embolism. It needs prompt medical care from a doctor. (Decompression sickness and barotrauma)

R

RAID

The Rebreather Association of International Divers. Wikipedia (secondary) says it was founded in 2007 to train divers on the Poseidon Mk VI Discovery rebreather and later added open circuit and other courses; sources disagree on whether it began in Sweden or Australia. (Training agencies)

Rebreather

Scuba that recycles exhaled gas, in closed or semi-closed circuit. Wikipedia (secondary) says rebreathers use less gas and make fewer bubbles than open circuit but are more complex and less widely used. The History of Diving Museum credits Henry Fleuss with the first functional one in 1876; other sources date his patent and first practical apparatus to 1878. (How scuba diving works)

Receiver of Wreck

The UK official, part of the Maritime and Coastguard Agency, to whom anyone who recovers wreck material from UK waters must report it within 28 days under the Merchant Shipping Act 1995, according to GOV.UK. (UK protected wrecks)

Recompression chamber

A hyperbaric chamber; DAN says suspected decompression illness is treated in one. DAN's 2020 position is that a diver with a suspected injury needs medical evaluation at a hospital or emergency clinic first, and it does not publish chamber availability because it changes often. (Dive insurance and chambers)

Recompression Chamber Network (RCN)

DAN's database of hyperbaric chambers that can and will treat injured divers, used by its doctors and hotline staff, as DAN's Alert Diver (2023) describes it. DAN says listing involves no financial arrangement. (Dive insurance and chambers)

Recreational depth limit

SSI, in an undated article, calls 40 m (130 ft) the generally accepted maximum recreational depth, and PADI's blog (updated May 2024) gives 40 m as the recreational limit for air diving without decompression stops; deeper diving falls under technical training. These are the agencies' statements, not rules for any diver. (Depth limits by certification)

Refraction

An optical effect of looking through water. PADI says refraction makes objects underwater look about 25 percent closer and 33 percent bigger. (Dive physics explained)

Regulator

The device that, as DAN describes it, turns high-pressure gas from the cylinder into gas at ambient pressure, through a first stage, an intermediate-pressure hose and a second stage. Servicing is for trained technicians, per PADI and DAN Europe. (Regulators)

Rescue Diver

The rescue-skills level that sits before professional training. PADI says its Rescue Diver requires Emergency First Response Primary and Secondary Care; NAUI's Rescue Scuba Diver requires current CPR, first aid and emergency oxygen certifications. (Certification levels)

Restoration Blueprint

NOAA's 2025 revision of Florida Keys sanctuary rules, published in the Federal Register on 17 January 2025. Keys Weekly reports that Florida's governor blocked it in state waters in March 2025 and that it took effect in federal waters on 5 March 2025. (Florida Keys)

RGBM (Reduced Gradient Bubble Model)

Dr Bruce Wienke's bubble decompression model, which Suunto says it adopted in the late 1990s (maker statement). A 2018 study by Doug Fraedrich classed Suunto-RGBM as a bubble model and found that none of the four algorithms it tested passed every test at factory settings. (Dive computers)

Rouquayrol-Denayrouze apparatus

A French demand-regulator breathing set of the 1860s. Wikipedia (secondary) calls the 1864 version the first diving suit to supply air on demand, though it still needed surface supply for useful endurance; Blutime says the French Navy tested it in 1864. (Before the Aqua-Lung)

RSTC

A Recreational Scuba Training Council: a national or regional group of training organisations. The US RSTC was created in 1986, per Wikipedia (secondary), and publishes minimum course standards. See WRSTC. (Training agencies)

Rule of thirds

A cave-diving gas management rule, named here only as history. The NSS Cave Diving Section credits Sheck Exley with proposing it in 1968, and the UK Cave Diving Group also credits him. (Cave and technical diving)

Rules of accident analysis

The causes Sheck Exley drew from cave-diving deaths in "Basic Cave Diving: A Blueprint for Survival" (1979): no continuous guideline to the exit, inadequate gas reserve and excessive depth, with inadequate training and inadequate lighting added in 1984, per InDepth (2025). The same 2025 article argues the analysis left out contributing factors. These are history, not instructions. (Cave and technical diving)

S

Sanctuary Preservation Area

A zone of the Florida Keys National Marine Sanctuary. NOAA's Restoration Blueprint FAQ says anchoring will be banned in all of them by 2027, with moorings required. (Florida Keys)

SCTLD

Stony coral tissue loss disease. STINAPA's diving rules allow diving throughout the Bonaire National Marine Park except in two reserves and at sites temporarily closed because of it. (Bonaire)

SCUBA

An acronym for self-contained underwater breathing apparatus. Sources tell its origin differently: the NAE tribute says a 1952 paper by Christian Lambertsen and a colleague described the apparatus that gave the acronym, Wikipedia (secondary) says he renamed his device SCUBA in 1952, and Dictionary.com dates the word to 1950 to 1955. (Lambertsen and the word scuba)

Scuba Diver (PADI)

A subset of PADI's Open Water Diver course. PADI's blog (2018) says it is limited to 12 m (40 ft) under the direct supervision of a PADI Professional, where an Open Water Diver may dive with a certified buddy. (Certification levels)

SDI and TDI

Technical Diving International and Scuba Diving International. TDI's story page says TDI was founded in 1994 for training beyond sport diving and SDI launched in 1998 as its sport diving division; sources disagree on TDI's co-founders and founding year. (Training agencies)

Second stage

The part of a regulator held in the mouth, which DAN says delivers gas at ambient pressure. DAN describes a dive or pre-dive switch on many second stages that makes them less likely to free-flow at the surface. (Regulators)

Self-Reliant Diver

PADI's solo-diving specialty, which PADI (2022) says requires age 18, Advanced Open Water and 100 logged dives, and which does not guarantee being allowed to dive alone. SDI's undated Solo Diver course page requires age 21. (Buddy and solo diving)

Sidemount

A configuration PADI describes as a back wing with a harness that carries cylinders at the diver's sides. (BCDs)

Silfra

A fissure in Iceland's Thingvellir National Park. Under Instructions No. 165/2013 as amended by Notice No. 207/2017, solo diving is banned, the maximum depth is 18 m, scuba in a wetsuit is prohibited, and dry-suit divers must show a dry-suit certification or 10 dry-suit dives in the previous two years. Divers need park permission under Rules No. 214/2013. (Silfra)

Solo diving

Diving without a buddy. SDI says it was once discouraged by most agencies but that many now accept it for suitably trained and experienced divers; Wikipedia (secondary) says a 2006 BSAC report judged the added risk of planned solo diving unacceptable, and that its true risk compared with buddy diving has never been reliably established. (Buddy and solo diving)

SPG (submersible pressure gauge)

The gauge that, as PADI describes it, shows how much gas is left in the cylinder, either hose-connected or built into a computer. A console combines it with a depth gauge or computer and a compass. (Dive computers)

SSI (Scuba Schools International)

A training agency SSI says was established in 1970; Wikipedia (secondary) says it merged with NASDS in 1999 and was acquired by HEAD, owner of the Mares brand, on 1 January 2014. SSI claims over 4,000 training centres in more than 150 countries (agency claim). (Training agencies)

Stabilizer jacket

An early wrap-around jacket BCD. Wikipedia (secondary) says ScubaPro introduced it in 1971, and ScubaPro's own timeline calls its 1971 jacket the industry's first, while other summaries of ScubaPro pages date the design to 1978; we could not confirm which is right. (The buoyancy jacket)

STINAPA

Stichting Nationale Parken Bonaire, which manages the Bonaire National Marine Park. Its rules require a nature fee valid for one calendar year, an orientation dive on arrival, and no gloves or knee pads, and bar touching marine life. Fee amounts are not given on this site. (Bonaire)

Sunken Military Craft Act 2004

A US law, signed on 28 October 2004, that the National Park Service says protects US government sunken military craft wherever they lie, and foreign ones in US waters, from unauthorised disturbance through a permit system. Its rules are in 32 CFR part 767. (US wreck law)

Supervised diver

Level 1 of ISO 24801 (ISO 24801-1:2014), covering diving under a dive professional's supervision. PADI's Scuba Diver (12 m in PADI's 2024 restrictions article) and NAUI's Scuba Diver (Supervised Diver, ISO Level 1; 12 m on an undated NAUI page) both carry a 12 m limit. (ISO diver standards)

Surface marker buoy (SMB)

An inflatable tube or buoy that makes a diver visible at the surface. PADI describes signal tubes as bright orange or yellow, more than a metre tall when inflated and required in many areas; DAN notes small ones can be hidden by waves. See also delayed surface marker buoy. (Lights and signalling)

Sustained load cracking

Cracking in the necks of some aluminium cylinders. Luxfer says its 6351-alloy cylinders were made in the US until mid-1988 and in England until 1995, after which it switched to 6061 alloy, which it says is not prone to it (maker statement); DAN's 2017 article gives 1989 as the end of 6351-T6 production. 49 CFR 180.209(m) requires a five-yearly eddy current check of 6351-T6 scuba cylinders. (Cylinder inspection and testing)

T

Technical diving

Diving beyond generally accepted recreational limits, with greater risk; one definition Wikipedia (secondary) offers is a dive where a direct vertical ascent to the surface is not possible at some point. Michael Menduno says he first used the term in aquaCORPS in January 1991. Wikipedia notes experts still disagree on exactly what counts. (Cave and technical diving)

Tissue compartments

The theoretical body tissues a decompression model tracks. PADI's blog (2026) says computers model gas uptake and release with them, some using 16; Suunto's Fused RGBM 2 uses 15 tissue groups (maker claim). (Dive computers)

TIV

France's technical visual inspection of diving cylinders. The FFESSM's December 2017 bulletin says that from 1 January 2018 cylinders inspected yearly under the TIV scheme may go 6 years between requalifications, against 2 years otherwise. (Cylinder inspection and testing)

Trigger

The first step in Denoble and colleagues' 2008 causal analysis of diving deaths: the event that started the chain. The most frequent triggers were insufficient gas (41 percent), entrapment (20 percent) and equipment problems (15 percent). (What the accident data shows)

Trilaminate

A dry-suit shell material of nylon and butyl rubber layers. DAN (2012) says technical divers often favour trilaminate shells, which give little insulation themselves, so warmth comes from undergarments. (Dry suits)

U

UHMS

The Undersea and Hyperbaric Medical Society. The NAE tribute credits Christian Lambertsen as founder of its predecessor, the Undersea Medical Society, in 1967 to 1968, while Wikipedia (secondary) names six US Navy medical officers. DAN says the UHMS hosts the 2020 Recreational Diving Medical Screening System forms. (Medical screening)

UKDMC

The UK Diving Medical Committee, formerly the UK Sport Diving Medical Committee: the medical advisers to BSAC, the Sub-Aqua Association and the Scottish Sub-Aqua Club. Members of those clubs complete a medical self-declaration every year, and any yes answer means contacting a UKDMC Medical Referee, a doctor who decides. (Medical screening)

Underwater Cultural Heritage Act 2018

An Australian law, enacted on 24 August 2018, that Wikipedia (secondary) says automatically protects shipwrecks that have been in Australian waters for 75 years or more, and replaced the Historic Shipwrecks Act 1976. (Wreck diving and the law)

UNESCO 2001 Convention

The Convention on the Protection of the Underwater Cultural Heritage, which makes preservation in place the first option and bars commercial exploitation of underwater heritage; its Annex holds 36 practical Rules. (Wreck diving and the law)

V

Visual inspection (cylinders)

An inspection of a cylinder between pressure tests. Luxfer's undated FAQ says DOT and the US scuba industry suggest a yearly visual for 6351-alloy cylinders, while 49 CFR 180.209 sets no annual visual for scuba; a search summary of PSI-PCI's site, which we could not open, describes annual visuals as required. BSAC (2020) gives an interim visual about two and a half years after the UK hydraulic test, and France's TIV is yearly (FFESSM, 2017). (Cylinder inspection and testing)

VPM-B

A bubble decompression model. Doug Fraedrich's 2018 study classed it as a bubble (dual-phase) model and found its first stop always deeper than his reference; sources disagree on the benefit of such deep stops. (Dive computers)

W

Weights and ditchable weights

Lead carried to offset the buoyancy of body and suit. PADI names weight belts, integrated BCD pockets and trim weights and lists a quick-release feature as standard; Wikipedia (secondary) separates ditchable weights, which can be released, from fixed weights. (Weights)

Wetsuit

Closed-cell neoprene exposure protection, 1 to 9 mm thick, per PADI. Sources disagree on how it keeps a diver warm: PADI says the body warms a thin layer of water the neoprene insulates, while DAN (2012) says it works mainly by limiting water flushing through. (Wetsuits)

Women Divers Hall of Fame

Founded in 1999 to honour women's contributions to diving, per Wikipedia (secondary), which says 72 women were inducted in the first class of 2000 and lists members including Sylvia Earle, Lotte Hass and Dottie Frazier. (Women in diving)

Wreck (UK legal meaning)

Section 255 of the UK Merchant Shipping Act 1995 defines wreck as jetsam, flotsam, lagan and derelict found in or on the shores of the sea or tidal water. GOV.UK says recovered wreck must be reported regardless of its age, size or value. (UK protected wrecks)

WRSTC

The World Recreational Scuba Training Council, founded in 1999 to develop worldwide minimum training standards. Its members are national or regional councils (Canada, Japan, the United States and Europe), each made of agencies covering at least half of that region's annual certifications. (Training agencies)