# Index of underwater diving: F–K

The following index is provided as an overview of and topical guide to underwater diving: Links to articles and redirects to sections of articles which provide information on each topic are listed with a short description of the topic. When there is more than one article with information on a topic, the most relevant is usually listed, and it may be cross-linked to further information from the linked page or section.
Underwater diving can be described as all of the following:
There are seven sub-indexes, listed here. The tables of content should link between them automatically:
* Index of underwater diving: A–C
* Index of underwater diving: D–E
* Index of underwater diving: F–K
* Index of underwater diving: L–N
* Index of underwater diving: O–R
* Index of underwater diving: S
* Index of underwater diving: T–Z

## F

| Contents: Top | 0–9 | A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z |
Section contents: Top of section, Fa, Fe, Fi, Fl–Fn, Fo, Fr, Fu

### Fa

* Faber Industrie S.p.A., also known as Faber Cylinders – Italian manufacturer of high pressure gas storage cylinders
* Faceplate (diving) – Transparent viewport on the front of a diving helmet or full-face mask
* Fatal scuba diving incidents – Deaths occurring while scuba diving or as a consequence of scuba diving

### Fe

Section contents: Top of section, Fa, Fe, Fi, Fl–Fn, Fo, Fr, Fu
* Feather breathing – Technique for minimising gas loss during some regulator malfunctions
* Federación Española de Actividades Subacuáticas (FEDAS) – Spanish national federation for underwater activities, affiliated to CMAS
* Fédération Française d'Études et de Sports Sous-Marins (FFESSM) – French diver training and certification agency
* Federazione Italiana Attività Subacquee (FIAS) – Italian non-profit recreational diver training organisation affiliated to CMAS
* Feet fresh water – Unit of pressure equal to 1/34 atm.
* Fenzy – French manufacturer of industrial and diving breathing equipment
* Fernez, Maurice – French inventor and pioneer in underwater breathing apparatus
* Ferraro, Luigi – Officer of the Royal Italian Navy and pioneer of Italian submarine warfare

### Fi

Section contents: Top of section, Fa, Fe, Fi, Fl–Fn, Fo, Fr, Fu
* Fibre wound composite cylinder – Pressure vessel with fibre structural reinforcement
* Fick's laws of diffusion – Mathematical descriptions of molecular diffusion
* Fife, William Paul – US Air Force officer and hyperbaric medicine researcher
* Filling whip – High pressure hose for filling compressed gas cylinders
* Fin retainer – Rubber straps for securing swimfins to the feet
* Finning technique – Skills used by divers and surface swimmers using swimfins
* Finswimming – Competitive watersport using swimfins for propulsion
* Finswimming at the 2001 World Games – Competition held in Akita, Japan
* Finswimming at the 2001 World Games – Men's 50 m apnoea – Competition held in Akita, Japan
* Finswimming at the 2005 World Games – Men's 50 m apnoea – Competition held in Duisburg, Germany
* Finswimming at the 2009 Asian Indoor Games – Competition held in Mỹ Đình National Aquatics Sports Complex, Hanoi, Vietnam
* Finswimming at the 2009 World Games – International competition in Kaohsiung
* Finswimming at the 2009 World Games – Men's 50 m apnoea – Event in Kaohsiung, Taiwan
* Finswimming at the 2011 SEA Games – Watersport competition in Palembang, Indonesia
* Finswimming at the 2021 SEA Games – Competition at Mỹ Đình Aquatics Center in Hanoi, Vietnam
* Finswimming at the 2023 SEA Games – Competitions held at Phnom Penh, Cambodia
* Finswimming at the World Games – Trend sport at the World Games
* Finswimming in Australia – Competitive watersport
* Finswimming in the United Kingdom – Competitive watersport
* Finswimming in the United States – Competitive watersport
* Finswimming World Championships – International event for the underwater sport of finswimming
* First aid – Emergency first response medical treatment
* Fischer, George R. – American underwater archaeologist
* Fitness to dive, also known as fitness for diving – Medical fitness to function underwater

### Fl–Fn

Section contents: Top of section, Fa, Fe, Fi, Fl–Fn, Fo, Fr, Fu
* Fleuss, Henry – British inventor of diving equipment (1851 – 1933)
* Flicker fusion threshold – Concept in the psychophysics of vision
* Flushing the loop – Rebreather diving safety procedure
* Flying after diving – Precautions against decompression sickness when ascending to altitude after diving
* FNRS-2 – First bathyscaphe
* FNRS-3 – Bathyscaphe of the French Navy

### Fo

Section contents: Top of section, Fa, Fe, Fi, Fl–Fn, Fo, Fr, Fu
* Force – Influence that can change motion of an object
* Formoza Military Unit – Polish Special Forces unit
* Forward dive profile – Repetitive dive shallower than the preceding dive

### Fr

Section contents: Top of section, Fa, Fe, Fi, Fl–Fn, Fo, Fr, Fu
* Fraction of inspired oxygen – Volumetric proportion of oxygen to other constituents in a breathing gas
* Franzén, Anders – Swedish marine technician and amateur naval archaeologist
* Free immersion apnea – Human-powered freediving discipline
* Free-flow diving helmet, also known as free-flow helmet – Helmet which supplies a continuous flow of air to the diver
* Freediving – Underwater diving without breathing apparatus
* Freediving blackout – Loss of consciousness caused by cerebral hypoxia towards the end of a breath-hold dive
* Freediving blackout of ascent – Hypoxic blackout while ascending from a deep breathhold dive
* Freediving computer – Worn unit for monitoring and recording freedive data
* Freediving training agency, also known as freediver training agency – Organisation for training and certifying the competence of freedivers
* Freeflow – A state of continuous flow of breathing gas in an underwater breathing apparatus
* Free-flow breathing apparatus – Equipment which provides a constant flow of breathing gas
* French commando frogmen – Combat swimmer unit of the French Navy
* Frenzel maneuver – Ear equalization technique originally developed for dive bomber pilots
* Fresh gas flow (disambiguation) – Gas added to the recycled gas of a rebreather or anesthetic machine
* Freshwater diving – Underwater diving in fresh water
* Freshwater diving environment – Type of underwater diving environment
* Frog kick – Finning propulsion kick used particularly by cave and wreck divers
* Frogman – Tactical scuba diver
* Frogman Corps (Denmark) – Danish maritime special operations unit
* FROGS (Full Range Oxygen Gas System) – Closed circuit oxygen diving rebreather
* fsw (pressure) – Hydrostatic pressure of a water column in terms of depth in feet

### Fu

Section contents: Top of section, Fa, Fe, Fi, Fl–Fn, Fo, Fr, Fu
* Fuerzas Especiales – Special forces unit of the Mexican Navy
* Fukuryu – Japanese divers intended to manually detonate mines on invading ships
* Full-face diving mask – Diving mask that covers the mouth as well as the eyes and nose
* Full facepiece – User respiratory inteface with breathing apparatus that covers the nose, mouth and eyes
* Full-face snorkel mask – Breathing apparatus for surface swimming
* Full ocean depth – Maximum known depth in the ocean

## G

| Contents: Top | 0–9 | A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z |
Section contents: Top of section, Ga, Ge, Gl, Go–Gp, Gr, Gu, Gy

### Ga

* Gaiters (diving) – Accessories used to restrict volume of a dry suit over the lower legs
* Gap line, also known as jump line – Line laid when crossing a gap between permanent cave lines
* Gas blender – Person who blends breathing gas mixtures for scuba diving and fills diving cylinders
* Gas blender level 1, also known as nitrox blender – Person competent to mix nitrox for scuba divers
* Gas blender level 2, also known as trimix blender – Person competent to mix trimix for scuba divers
* Gas blending – Producing special gas mixtures to specification
* Gas blending for scuba diving – Mixing and filling cylinders with breathing gases for use when scuba diving
* Gas booster – Machine to increase the pressure of compressed gas
* Gas capacity – Amount of gas that can be stored in a container
* Gas cylinder – Cylindrical container for storing pressurised gas
* Gas cylinder bundle, also known as gas cylinder quad – Group of manifolded gas cylinders mounted on a transport frame
* Gas diving – Underwater diving using air as the breathing gas
* Gas endurance – The time a gas supply will last
* Gas exchange – Process by which gases diffuse through a biological membrane
* Gas extender – Type of semi-closed circuit diving rebreather
* Gas-integrated dive computer – A dive computer that displays the pressure of breathing gas remaining in the cylinder
* Gas integration – Facility for a dive computer to display breathing gas cylinder pressures
* Gas laws – List of physical laws relates to gases
* Gas man, also known as gas panel operator – Member of a surface-supplied diving team who operates the breathing gas panel
* Gas matching – Ensuring that reserve breathing gas is sufficient to supply the dive buddy
* Gas panel – Breathing gas distribution panel for surface-supplied diving
* Gas panel operator, also known as gas man – Member of a surface-supplied diving team who operates the breathing gas panel
* Gas-reclaim system – Equipment to recover exhaled gas from a diver to save the helium content
* Gas storage bank – Manifolded group of gas storge cylinders
* Gas storage cylinder – Container for storing pressurised gas
* Gas storage quad – Group of similar size high pressure cylinders
* Gas storage tube – Large volume, high pressure gas storage cylinder
* Gas switch – Change of breathing gas mixture during a dive
* Gas switching – Changing the breathing gas mixture during a dive
* Gas toxicity – Dose dependent harmfulness of gases
* Gay-Lussac's law – Relationship between pressure and temperature of a gas at constant volume

### Ge

* German commando frogmen – German postwar commando amphibious warfare force

### Gl

Section contents: Top of section, Ga, Ge, Gl, Go–Gp, Gr, Gu, Gy
* Global Explorer ROV – Deep water science and survey remotely operated vehicle
* Global Underwater Explorers (GUE) – Recreational/technical scuba training and certification agency
* Glossary of breathing apparatus terminology – Definitions of technical terms used in connection with breathing apparatus
* Glossary of underwater diving terminology, also known as Glossary of underwater diving terms or Glossary of SCUBA diving
* Glossary of underwater diving terminology: A–C
* Glossary of underwater diving terminology: D–G
* Glossary of underwater diving terminology: H–O
* Glossary of underwater diving terminology: P–S – List of terms used in underwater diving and their meanings in context
* Glossary of underwater diving terminology: T–Z

### Go–Gp

Section contents: Top of section, Ga, Ge, Gl, Go–Gp, Gr, Gu, Gy
* Goldfinder – Autobiography of British diver and treasure hunter Keith Jessop
* Gold line (diving) – Permanent main guide line in a cave
* Gold Rush: White Water – American television series
* Goldfish-class ROUV – Light class of Chinese remotely operated underwater vehicle
* Goldman Interconnected Compartment Model – Decompression model proposed by Saul Goldman
* Goodman handle – Mounting which holds a dive light on the back of the diver's hand
* Gorski (diving helmet) – Diving helmet brand owned by Aqualung Group
* GPS sonobuoy, also known as GPS intelligent buoy – Acoustic positioning devices

### Gr

Section contents: Top of section, Ga, Ge, Gl, Go–Gp, Gr, Gu, Gy
* Gradient factor – Method for adjusting conservatism of decompression algorithms
* Gradient factor in decompression modelling – A way for users to adjust the conservatism of a decompression algorithm in software
* Green Fins – Organisation in South East Asia for preservation of coral reefs by improving diver behavior
* GROM Military Unit – Polish special forces unit
* GRUMEC, also known as Brazilian commando frogmen – Brazilian Navy special forces diving unit

### Gu

* Guide line – Line deployed by scuba divers for navigation

### Gy

* Gyrojet – Firearm that fires small rocket projectiles

## H

| Contents: Top | 0–9 | A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z |
Section contents: Top of section, Ha–Hb, He, Hi, Ho, Hu, Hy

### Ha–Hb

* Haenyeo – Female divers of Jeju, South Korea
* Halcyon Dive Systems – American manufacturer of diving equipment
* Halcyon PVR-BASC – Semi-closed circuit depth compensated passive addition diving rebreather
* Halcyon RB80 – Non-depth-compensated passive addition semi-closed circuit rebreather
* Haldane, John Scott – British physiologist and decompression researcher (1860–1936)
* Haldane's decompression model – Decompression model developed by John Scott Haldane
* Half + 15 bar – Rule of thumb for scuba gas management
* Half mask – Diving mask covering the nose and eyes
* Half time (physics) – The time taken for a quantity to decrease by half in an exponential decay process
* Halocline – Stratification of a body of water due to salinity differences
* Hamilton, Robert William Jr. – American physiologist and researcher in hyperbaric physiology.
* Hand-held sonar – Ranging and imaging units for use by divers
* Hand-off a cylinder – Transfer a scuba cylinder from one diver to another in the water
* Hand-off cylinder – Scuba set that can be passed to another diver
* Hang-off profile – Commercial dive profile to limit ingassing during idle periods
* Hans Hass Award – Award in recognition of contribution made to the advancement of knowledge of the ocean
* Hans Hass – Austrian biologist, film-maker, and underwater diving pioneer
* Harasib Cave – Flooded karst cave in Namibia
* Hawaiian sling – Simple form of underwater speargun
* Hazard – Situation or object that can cause harm
* Hazard analysis (HAZID) – Method for assessing risk
* Hazard elimination – Hazard control by removing the hazard
* Hazard substitution – Replacing a material or process with a lower risk alternative
* Hazardous Materials Identification System – Numerical hazard rating using colour coded labels
* Hazards of the aquatic environment – Hazards inherent to being underwater
* Hazards of the diving environment – Dangerous conditions typical of places people dive
* Hazards of the specific diving environment – Factors which vary between diving environments
* Hazmat diver – Professional diver working in hazardous materials environments
* Hazmat diving – Underwater diving in a known hazardous materials environment
* Hazmat diving decontamination – Removing hazardous environmental contaminants from the diver after a dive
* H-BRUV – Horizontally aligned baited remote underwater video

### He

Section contents: Top of section, Ha–Hb, He, Hi, Ho, Hu, Hy
* Health and Safety Executive (HSE) – United Kingdom government agency
* Healthways (scuba gear company) – Defunct firm which made scuba gear
* Heckler & Koch P11 – Five-barreled underwater rocket dart pistol
* Heinke (diving equipment manufacturer) – British manufacturer of diving equipment
* HeinrichsWeikamp – German manufacturer of dive computers and other electronics for recreational diving
* Helgoland Habitat – Ambient pressure underwater habitat
* Heliair – Breathing gas mixed from air and helium
* Helicopter Aircrew Breathing Device, also known as helicopter escape set – Small scuba device for escape from ditched helicopters
* Helicopter turn – Rotation about a vertical axis by an underwater diver using only fins
* Heliox – A breathing gas mixed from helium and oxygen
* Heliox diving – Use of helium/oxygen breathing gas mix in underwater diving
* Helium analyzer, also known as helium analyser – Instrument to measure the concentration of helium in a gas mixture
* Helium reclaim system – System for recovering exhaled breathing gas
* Helium release valve – Feature on some watches for saturation diving
* Helium speech unscrambler – Technology for reducing hyperbaric speech distortion
* Helium tremors – Disorder from breathing helium based gas
* Helix Energy Solutions Group – Provider of offshore services and ROV operations
* Helmet squeeze – Injury caused low pressure in diving helmet
* Helmet weight – Ballast added to a diving helmet to prevent it from floating
* Hempleman, Henry Valence – British decompression researcher
* Henry's law – Gas law regarding proportionality of dissolved gas

### Hi

Section contents: Top of section, Ha–Hb, He, Hi, Ho, Hu, Hy
* Hierarchy of hazard controls – System used in industry to eliminate or minimize exposure to hazards
* High energy coast – Shoreline exposed to high energy waves
* High energy underwater environment – Underwater environment with high kinetic energy of the water
* High pressure breathing air compressor – Machine to fill cylinders with atmospheric air at high pressure for breathing
* High-pressure gas storage cylinder, also known as high pressure storage cylinder – Pressure vessel for storage of high pressure gas
* High-pressure nervous syndrome, also known as high-pressure neurological syndrome – Disorder from breathing helium based gas
* High-pressure water jetting – Cleaning method using very high pressure water jet
* Hill, Leonard Erskine – British physiologist (1866–1952)
* Hills, Brian Andrew – Physiologist who worked on decompression theory
* History of decompression research and development – Chronological list of notable events in the history of diving decompression.
* History of dive computers – Development of instruments to calculate decompression status in real time
* History of Diving Museum – Museum of underwater diving in Islamorada, Florida
* History of scuba diving – Origins and development of diving using breathing gas carried by the diver
* History of underwater diving – Developments over time in the human activity

### Ho

Section contents: Top of section, Ha–Hb, He, Hi, Ho, Hu, Hy
* Hog looped – Scuba regulator long hose configuration
* Hogarthian scuba configuration – Scuba harness arrangement developed by Bill Main
* Hoke valve – Gas recirculation control valve on MK V helium hemet
* Hookah (diving) – Basic surface supplied equipment using an air-line
* Hookah diving – Underwater diving using a basic air hose from the surface
* Hoppe-Seyler, Felix – German physiologist and chemist (1825–1895)
* Hot stab – Type of subsea quick connector for offboard services
* Hot water suit – A wetsuit with a supply of heated water to keep a diver warm
* Hot water system (diving) – Water heating and supply system for hot-water diving suits

### Hu

Section contents: Top of section, Ha–Hb, He, Hi, Ho, Hu, Hy
* Huggins, Karl E. – American decompression researcher
* Human factors in diving equipment design – Influence of the interaction between the user and the equipment on design
* Human factors in diving safety – The influence of physical, cognitive and behavioral characteristics of divers on safety
* Human factors in the design of diving equipment – Influence of the interaction between the user and the equipment on design
* Human physiology of underwater diving, also known as human physiology of diving – Influences of the underwater environment on the physiology of human divers
* Human torpedo – Early form of diver propulsion vehicle

### Hy

Section contents: Top of section, Ha–Hb, He, Hi, Ho, Hu, Hy
* Hydraulic chainsaw – Chainsaw powered by a hydraulic motor
* Hydreliox – Breathing gas mixture of hydrogen, helium, and oxygen
* Hydrocleaning – Use of a water jet for cleaning hard surfaces
* Hydrogen narcosis – Psychotropic state induced by breathing hydrogen at high partial pressures
* Hydrogen sulfide – Poisonous, corrosive and flammable gas
* Hydrophobe – Molecule or surface that has no attraction to water
* HydroSpace Engineering – US manufacturer of decompression computers
* Hydrostatic pressure – The static pressure exerted by the weight of the fluid column above the point
* Hydrostatic test – Non-destructive test of pressure vessels
* Hydrox (breathing gas) – Breathing gas mixture experimentally used for very deep diving
* Hyperbaric escape capsule – Small hyperbaric evacuation unit that drifts until rescued
* Hyperbaric evacuation – Emergency transport of people in a hyperbaric chamber
* Hyperbaric evacuation and rescue – Emergency transport of divers under a decompression obligation to a place of safety
* Hyperbaric evacuation facilities – Systems to evacuate saturation divers in an emergency
* Hyperbaric evacuation system – Equipment for emergency transport of divers under pressure to a place of safety
* Hyperbaric evacuation unit – Pressure vessel in which divers are transported under pressure in an emergency
* Hyperbaric lifeboat – Lifeboat for transporting people under pressure
* Hyperbaric medicine – Medical treatment at raised ambient pressure
* Hyperbaric nursing – Nursing specialty in hyperbaric oxygen therapy
* Hyperbaric oxygen therapy chamber – Pressure vessel for human occupancy used in hyperbatic medicine
* Hyperbaric oxygen treatment – Medical oxygen treatment at raised pressure
* Hyperbaric oxygen treatment table – Planned hyperbaric exposure using oxygen breathing gas as medical treatment
* Hyperbaric reception facility – Saturation facility on standby in case evacuation is necessary
* Hyperbaric rescue – Emergency transport of people in a hyperbaric chamber
* Hyperbaric rescue chamber – Hyperbaric chamber suitable for emergency transport of divers under pressure
* Hyperbaric rescue vessel – Ship to recover hyperbaric evacuation units
* Hyperbaric speech distortion – Speech distortion at high ambient pressure
* Hyperbaric stretcher – Portable pressure vessel to transport a person under pressure.
* Hyperbaric transport – Transportation under pressure greater than atmospheric
* Hyperbaric transportation – Transport under pressure greater than atmospheric
* Hyperbaric treatment – Medical treatment at raised ambient pressure
* Hyperbaric treatment schedules – Planned hyperbaric exposure using a specified breathing gas as medical treatment
* Hyperbaric treatment tables – Planned hyperbaric exposure using a specified breathing gas as medical treatment
* Hyperbaric welding – Welding metal at elevated pressure
* Hypercapnia – Abnormally high tissue carbon dioxide levels
* Hyperoxia – Exposure of tissues to abnormally high concentrations of oxygen.
* Hyperoxic breathing gas – Gas mixture with higher oxygen content than air
* Hyperoxic myopia – Short sightedness caused by exposure to high oxygen concentrations
* Hyperthermia – Elevated body temperature due to failed thermoregulation
* Hyperventilation – Excessive breathing
* Hyperventilation-induced blackout – Loss of consciousness caused by cerebral hypoxia towards the end of a breath-hold dive
* Hypobaric decompression – Reduction in pressure to lower than normal sea level atmospheric pressure
* Hypocapnia – State of reduced carbon dioxide in the blood
* Hypothermia – Human body core temperature below 35 °C (95 °F)
* Hypoventilation – Insufficient breathing
* Hypoxia (medicine) – Medical condition of lack of oxygen in the tissues
* Hypoxia of ascent – Loss of cosciousness during ascent from a breathhold dive
* Hypoxic blackout – Loss of consciousness due to cerebral hypoxia
* Hypoxic breathing gas – Gas mixture with lower oxygen content than air
* Hypoxic trimix – Gas mixture of helium, nitrogen and insufficient oxygen to safely breathe at surface pressure
* Hypoxic trimix diver – Recreational technical diving certification level

## I

| Contents: Top | 0–9 | A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z |
Section contents: Top of section, Ic, Id, Im, In, Ir–Is, It

### Ic

* Ice diving – Underwater diving under ice
* Ichthyander Project – Soviet underwater habitat project of the 1960s
* Ictineu 3 – Crewed submersible

### Id

Section contents: Top of section, Ic, Id, Im, In, Ir–Is, It
* IDA71 – Russian military rebreather for underwater and high altitude use
* Ideal gas law – Equation of the state of a hypothetical ideal gas
* IDRCF – International Diving Regulators and Certifiers Forum

### Im

Section contents: Top of section, Ic, Id, Im, In, Ir–Is, It
* IMCA – International trade association for the marine contracting industry
* IMCA Code of Practice for Offshore Diving, also known as IMCA D014 – Guidance document for member organisations
* IMCA Diving Supervisor's Manual, also known as IMCA D022 – Procedures endorsed by IMCA for offshore diving operations
* IMCA Safety flash – Anonymised incident reports
* Immersion finswimming – Competitive scuba watersport using swimfins for propulsion
* Immersion finswimming with breathing apparatus – Competitive scuba watersport using swimfins for propulsion
* Immersion pulmonary oedema – Body fluid accumulated in the lungs due to immersion in a liquid
* Immersion response – The physiological responses to immersion of air-breathing vertebrates

### In

Section contents: Top of section, Ic, Id, Im, In, Ir–Is, It
* Incident pit – Conceptual model for explaining incident development and recovery
* Independent doubles, also known as independent twin cylinders – Two fully redundant back-mounted scuba sets with no cross-connection
* Index of recreational dive sites – Alphabetical listing of articles on porular places for recreational diving
* Index of underwater divers – Alphabetical listing of articles about underwater divers
* Index of underwater diving – Alphabetical listings of underwater diving related topics
* Industrie Werke Karlsruhe Aktiengesellschaft (IWKA) – German manufacturer of seamless steel gas cylinders
* Inert gas counterdiffusion – Diffusion of one inert gas into body tissues while another inert gas is diffusing out
* Ingassing – Uptake of gases by biological tissues
* Inherent unsaturation – Physiological effect of oxygen metabolism on the total dissolved gas concentration in venous blood
* Inland dive site – Sites in bodies of water inland of the sea coastline
* Inland diving – Diving in waters inland of the coastal high water mark.
* Inner ear barotrauma – Pressure injury to the inner ear
* Inner ear decompression sickness – Medical condition caused by inert gas bubbles forming out of solution
* Inshore diving – Diving in coastal territorial waters
* Instinctive drowning response – Instinctive reaction that occurs in humans when close to drowning
* Insulán, Stig – Inventor of an adjustable automatic exhaust valve for variable volume dry suits
* Integrated Diver Display Mask – Diving half-mask with integrated head-up instrument display
* Integrated weight system – Diver weights carried on the buoyancy compensator or safety harness
* Integrated weights – Diving weights carried in pockets on the buoyancy compensator
* Intelligent Water class AUV – Autonomous underwater vehicle for the People's Liberation Army Navy
* International Association for Handicapped Divers (IAHD) – Non-profit organisation based in the Netherlands
* International Association of Nitrox and Technical Divers (IANTD) – Recreational and technical scuba training and certification agency
* International Bluewater Spearfishing Records Committee – Committee of special interest
* International Coral Reef Society – Non-profit scientific society for the conservation of coral reefs.
* International Divers Alert Network – Independently administered nonprofit DAN regional organizations
* International Diving Institute – American commercial diver training school
* International Diving Regulators and Certifiers Forum (IDRCF), also known as International Diving Regulators Forum – International forum of professional diver accreditation organisations
* International Diving Schools Association (IDSA) – Organisation to develop common standards for commercial diver training
* International Life Saving Federation – Umbrella organization of the national lifesaving organizations
* International Marine Contractors Association (IMCA) – International trade association for the marine contracting industry
* International Organization for Standardization (ISO) – International standards development organization
* International Scuba Diving Hall of Fame – Annual event recognizing recreational scuba industry contributors
* International Submarine Escape and Rescue Liaison Office – Organization that coordinates international submarine search and rescue operations.
* International Underwater Cave Rescue and Recovery – Cave diving rescue/recovery organization
* Interspiro – Swedish manufacturer of breathing apparatus
* Interspiro DCSC – Military semi-closed circuit passive addition diving rebreather
* Intervention AUV – Type of autonomous underwater vehicle capable of autonomous interventions
* Intestinal squeeze – Injury to intestines by expanding gas during decompression
* Introductory diving – Non-certification scuba diving experience
* Introductory scuba experience – Non-certification scuba diving experience
* Investigation of diving accidents – Forensic investigation of underwater diving accidents
* In-water cleaning – Methods of removing contaminants from underwater surfaces
* In-water recompression – In-water treatment for decompression sickness
* In-water surface cleaning – Methods of removing contaminants from underwater surfaces
* In-water recompression – In-water treatment for decompression sickness

### Ir–Is

Section contents: Top of section, Ic, Id, Im, In, Ir–Is, It
* iRobot Seaglider – Deep diving autonomous underwater vehicle for long term missions
* iSimangaliso Marine Protected Area – Marine conservation area in northern kwaZulu-Natal in South Africa
* Isobaric counterdiffusion – Gaseous diffusion through body tissue at constant total pressure
* Isolation manifold – Upstream scuba manifold with a shut-off valve
* Isolation-manifolded twin cylinders, also known as isolation-manifolded twin set – Scuba set with two back-mounted cylinders connected by a manifold with an isolation valve
* ISO 24801 Recreational diving services — Requirements for the training of recreational scuba divers – International training standards for recreational scuba
* ISO recreational diving standard – International standards for recreational diver competence
* ISO recreational diving training standards – Publications of the International Standards Organisation
* Israeli Diving Federation (TIDF) – Israeli recreational diver training and certification agency

### It

* Italian auxiliary ship Olterra – Undercover Italian auxiliary ship from World War II

## J

| Contents: Top | 0–9 | A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z |
* Jacket harness – Type of surface-supplied diving safety harness
* Jackstay – Substantial line between two points used to guide or support
* Jackstay (diving) – Substantial underwater guide line
* Jackstay search – Underwater search along a laid down line
* Jagdkommando – Austrian Armed Forces' Special Operations group
* JAGO (German research submersible) – Crewed German research submersible
* Jednostka Wojskowa Komandosów, also known as Commandos Military Unit – Polish special forces unit
* Jersey upline – A buoyed line serving as a position control during decompression
* Jetsam Technologies – Manufacturer of manual closed circuit rebreathers
* JIM suit – Type of atmospheric diving suit.
* Job safety analysis (JSA) – Procedure to integrate safety practices into a particular task
* Jocking harness, also known as jocking strap – System to manage buoyancy of a diver's helmet
* Johnson Sea Link accident – Manned submersible incident in which two divers died
* Jonline – A short line used by scuba divers to clip themselves to something
* Josef Heiser – Austrian manufacturer of seamless steel gas cylinders
* Jump camera – Camera triggered by landing on the bottom of a body of water
* Jump jacket – Surface-supplied diving safety harness with buoyancy compensation
* Jump line, also known as gap line – Line laid when crossing a gap between permanent cave lines
* Jump spool – Diving navigation and safety equipment
* Junior Open Water Diver – Entry level scuba certification for ages 10 to 14
* Just culture – Balanced accountability for both individuals and the organization
* J-valve – Type of scuba cylinder valve with reserve lever

## K

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* Kaikō ROV – Japanese remotely operated underwater vehicle for deep sea exploration
* Kaşif ROUV – Turkish remotely operated underwater vehicle
* Klingert, Karl Heinrich – German mechanic and inventor of an early surface-supplied diving suit.
* Karst Underwater Research – Non-profit organization that specializes in the research and documentation of karst aquifers
* Kayak diving – Recreational diving from a canoe or kayak
* Keel weight (diving) – Weight added to a diver's backplate
* Kelly (gas storage) – Large volume high pressure gas storage tubes
* Kilsby sinkhole – Sinkhole in Mount Gambier, Southern Australia
* Kimiuo Aisek Memorial Museum – Museum in Chuuk State, Federated States of Micronesia
* KISS Classic – Back mount manually controlled closed circuit rebreather
* KISS GEM – Back mount semi-closed circuit rebreather
* KISS Rebreathers – Brand of recreational diving rebreathers
* KISS Sidekick – Side mount manually controlled closed circuit or semi-closed circuit rebreather
* KISS Sidewinder – Symmetrical side mount manually controlled closed circuit rebreather
* Kiss Spirit – Lightweight back mount manually controlled closed circuit rebreather
* KISS (rebreather) – Manufacturer of recretional/technical mixed gas rebreathers
* Kommando Spezialkräfte Marine, also known as Kampfschwimmer – German postwar commando amphibious warfare force
* Kongsberg Mesotech – Manufacturer of sonar equipment for underwater imaging and detection
* Konsul-class submersible – Russian Navy deep sea submergence vehicle
* KOPASKA – Indonesian Navy special operations and demolition unit
* Kreeft, Peter – 18th Century German inventor and diver
* Kronan (ship) – Swedish Navy ship of the 1670s
* Kursk submarine disaster salvage operation – Raising the wreck of a Russian nuclear submarine
* K-valve – Plain single outlet scuba cylinder valve
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