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Glossary of underwater diving terminology: H–O
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This is a glossary of technical terms, jargon, diver slang and acronyms used in underwater diving. The definitions listed are in the context of underwater diving. There may be other meanings in other contexts.
Underwater diving can be described as a human activity – intentional, purposive, conscious and subjectively meaningful sequence of actions. Underwater diving is practiced as part of an occupation, or for recreation, where the practitioner submerges below the surface of the water or other liquid for a period which may range between seconds to the order of a day at a time, either exposed to the ambient pressure or isolated by a pressure resistant suit, to interact with the underwater environment for pleasure, competitive sport, or as a means to reach a work site for profit, as a public service, or in the pursuit of knowledge, and may use no equipment at all, or a wide range of equipment which may include breathing apparatus, environmental protective clothing, aids to vision, communication, propulsion, maneuverability, buoyancy and safety equipment, and tools for the task at hand.
Many of the terms are in general use by English speaking divers from many parts of the world, both amateur and professional, and using any of the modes of diving. Others are more specialised, variable by location, mode, or professional environment. There are instances where a term may have more than one meaning depending on context, and others where several terms refer to the same concept, or there are variations in spelling. A few are loan-words from other languages.
There are five sub-glossaries, listed here. The tables of content should link between them automatically:
- 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
- Glossary of underwater diving terminology: T–Z
H
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Contents: Top |
Subsection: Top, Ha, He, Hi, Ho, Hu
Ha
- habitat
An underwater structure inside which divers can carry out dry welding or which is fitted out with life support facilities.[1]
- Haldanean
- Haldanian
Decompression models based on the principles described by John Scott Haldane.
- half+200
- half+15
An alternative scuba reserve gas management strategy to the rule of thirds for breathing stage cylinders. The cylinder is breathed down to half of its starting pressure plus 200 psi (or 15 bar), so that a stage cylinder filled to 3000 psi would be breathed down to 1700 psi before being dropped.[2] Primary cylinder gas (usually back gas) is retained for use in contingencies.[3]
- half duplex
Voice communications system where users take turns to send and receive.[4]
- half mask
Diver's mask which covers the eyes and nose but not the mouth.
- half times
- halocline
A strong variation in salinity over a small depth range within a body of water. Often visible as a blurred or shimmering region due to uneven refractive index.[5]
- hand-off cylinder
- A diving cylinder, complete with regulator, which can be handed off (manually transferred) to another diver in an emergency, so that the two divers are not obliged to remain in close proximity during the exit and ascent. Transfer of a hand-off cylinder should not compromise either diver's buoyancy to the extent that they cannot make a normal, controlled ascent at neutral buoyancy.
- hang
- To remain stationary at a specific depth and location, particularly when decompressing.[2]
- hang-off
- hang off
Commercial diving procedure where the diver ascends to a shallower depth to minimise in-gassing during periods of waiting for surface support. The diver generally ascends to 30 ft waiting depth, and bottom time at that depth is not counted towards decompression obligation. When the support is ready, the diver returns to working depth and time elapsed from leaving hang-off depth accumulates towards decompression obligation. The profile appearance approximates a square wave form, or yo-yo profile.[6]
- hard hat diving
- Surface supplied diving, generally in professional diving, either wearing a modern diving helmet or the old-style standard diving dress with copper helmet.
- hardwire communications
- Voice communications using a cable for transmission.
- harness
- Straps and webbing with associated buckles, D-rings and other accessories used to support the breathing apparatus and secure it to the diver. The harness often has other functions such as supporting weighting and buoyancy control systems and for recovery of the diver from the water. In professional diving the harness is used as a strong point to attach the lifeline or umbilical to the diver.[1]
- hat
- Commercial diver term for diving helmet.
- HAZID
- Hazard identification study: A systematic qualitative assessment of potential hazards and threats to health, safety, equipment, property, environment, production, or reputation. May be followed by a risk assessment.
- hazmat diving
Diving in a known hazardous materials environment. The environment may be contaminated by hazardous materials, the diving medium may be inherently a hazardous material, or the environment in which the diving medium is situated may include hazardous materials with a significant risk of exposure to these materials to members of the diving team. Special precautions, equipment and procedures are associated with hazmat diving.
Subsection: Top, Ha, He, Hi, Ho, Hu
He
- head-up display
A visual display mounted where it is normally in the diver's field of vision.[7]
- Health and Safety Executive
UK government department responsible for occupational diver safety in UK.
- heavy gear
- heliair
Trimix blends made by topping up helium with air.[8]
- helicopter turn
- Manoeuver in which a horizontally trimmed diver uses small fin movements to rotate on the spot on a vertical axis.
- heliox
Mixtures of helium and oxygen for use as a breathing gas.[9][8]
- helium
An inert gas which is used as a component of breathing gas mixtures for deep diving.
- helium analyzer
An instrument used to identify the presence and concentration of helium in a mixture of gases
- helium unscrambler
- helium speech unscrambler
- helmet diving
- Henry's law
Description of the changes in solubility of a given gas in a given liquid as pressure varies.
Subsection: Top, Ha, He, Hi, Ho, Hu
Hi
- HID light
- High intensity discharge light: Used in cave diving light heads (q.v.).
- HIRA
- Hazard Identification and Risk Analysis: A risk management procedure for identifying hazards and assessing the risk associated with them and ways to reduce the risk to an acceptable level.
Subsection: Top, Ha, He, Hi, Ho, Hu
Ho
- Hogarthian configuration
- A scuba combination of backplate, wing, one-piece harness with crotch-strap, regulator arrangement including long-hose primary with a necklaced secondary demand valve, and, if used with twin cylinders, an isolation manifold. Named after William Hogarth Main, a developer and proponent of the system.[5]
- Hog looped
- Hogarthian loop
A scuba configuration where the primary demand valve has a long hose which is routed under the right arm, usually tucked under a light battery canister on the waist belt of the harness, and around behind the neck to reach the mouth from the right hand side. Part of the Hogarthian configuration (q.v.).[5]
- Hoke valve
Valve on the US Navy MK V helium helmet. The gas supply at the diver was controlled by two valves. The "Hoke valve" controlled flow through the injector to the "aspirator" which circulated gas from the helmet through the scrubber, and the main control valve used for bailout to open circuit, flushing the helmet, and for extra gas when working hard or descending.[10]
- hold-back line
- hold-back rigging
- Rigging provided to restrain excessive buoyancy of a lifting bag when it is attached to the load and inflated.[1]
- homebrew
- Amateur blended mixed gas.[5]
- hood
- Close-fitting thermal head protection, usually neoprene foam, but also latex on some dry suits.
- hook breathing
- hooka
- hookah
- hopcalite
Catalyst sometimes used in breathing air compressor filters to oxidise carbon monoxide to carbon dioxide. Hopcalite is a mixture of manganese oxide, copper oxide and a small amount of silver oxide.
- horse collar
- hose dash size
- Number indicating the bore of a hose in multiples of 1/16" preceded by a dash. for example a –04 hose, typically used for a pneumofathometer hose would have a nominal bore of 1⁄4 inch (6.4 mm). [11]
- hose organiser
Equipment to position and stabilise a hose, particularly in the context of sidemount or sling mounted scuba cylinders, where the regulator air hoses are stored against the cylinder when not in use.
- hot mix
- A breathing gas mixture with a high percentage of oxygen for the depth at which it is used. Using a gas mixture with a high partial pressure of oxygen.
- hot stab connector
- hot stab coupling
Quick connection coupling that can be connected by an ROV underwater, often to provide hydraulic power. The hot stab is the connector unit supplying the utilities, and it is usually inserted into a port after pulling out the plug stab, which is used to protect the port when it is not in use. Typically the alignment is not critical and the port will guide the stab in as it has concentric flow channels and o-ring seals. It may lock into place when fully inserted, or may require an external force to hold it in place while in use.[12][13][14]
- hot water suit
A loose fitting wetsuit supplied with heated water through a hose in the diver's umbilical, which links the diver to the surface support. The diver controls the flow rate of the water, allowing them to vary the warmth of the suit.[15][16]
- HP
- High pressure, generally gas pressures in excess of 30 bar. In most of the world a high pressure diving cylinder is a 300 bar cylinder, but in the US it may refer to anything over 3000 psi working pressure. In a diving context gas working pressures do not frequently exceed 300 bar, but pressures in hydraulic systems and high pressure water jetting equipment may be considerably higher.
- HPNS
- high-pressure nervous syndrome
A neurological and physiological diving disorder that occurs when a diver descends below about 500 feet (150 m) while breathing a helium–oxygen mixture.[17]
- HRC
- 1. See: hyperbaric rescue capsule
- 2. See: hyperbaric rescue chamber
- HRU
- HSE
Subsection: Top, Ha, He, Hi, Ho, Hu
Hu
- HUD
- H-valve
Cylinder valve body with two outlets and two valve mechanisms which can be independently controlled so that two regulator first stages can be fitted. Similar to Y-valve but in configuration where the second valve is parallel to the primary, though the secondary valve can sometimes be swivelled.
- hydro
- Slang/abbreviation for hydrostatic test (q.v.)[5]
- hydrophobic membrane
- A membrane that is freely permeable to gas but does not allow the passage of water at low pressure differentials. Used in some rebreather scrubbers to keep water from the absorbent material[7]
- hydrostatic pressure
Pressure due to the weight of the water column above a point at depth.[18]
- hydrostatic test
Non-destructive test to revalidate pressure vessels which uses water as a test medium. The vessel is pressurised to the test pressure (q.v.) and measured for permanent set.[19]
- hydreliox
Deep diving breathing gas mixture of hydrogen, helium and oxygen.[20]
- hydrox
Deep diving breathing gas mixture of hydrogen and oxygen.[20]
- hyperbaric evacuation
Evacuation of divers under pressure from a saturation chamber to a hyperbaric rescue craft via a pressurised transfer system.[1]
- hyperbaric evacuation system
System for evacuating divers under pressure from a saturation system in an emergency.[21] The whole system set up to provide hyperbaric evacuation, including planning, procedures, equipment used for evacuation, reception facility, contingency plans, possible safe havens and anything else requited for a successful hyperbaric evacuation.[1]
- hyperbaric lifeboat
A lifeboat with a hyperbaric chamber and life support system built into it for evacuating saturation divers in an emergency.[22]
- hyperbaric rescue capsule
- A self contained buoyant hyperbaric chamber intended for emergency evacuation of saturation divers under pressure from a platform which has become so dangerous that it is considered safer to put the divers into the sea in the HRC to be picked up by a rescue vessel for transfer to another hyperbaric system for decompression.[23]
- hyperbaric rescue chamber
- Normally a pressure vessel adapted to function as a means of hyperbaric evacuation with buoyancy chambers and lifting points, but not fitted in a lifeboat hull.[1]
- hyperbaric rescue facility
- hyperbaric reception facility
A unit which allows for connection of hyperbaric lifeboats and hyperbaric rescue capsules. Usually modular and portable so they can be moved to a suitable venue for standby with the hyperbaric rescue vessel.[24]
- hyperbaric rescue unit
- hyperbaric evacuation unit
Generic term for the unit provided to evacuate divers from a saturation system. It may be an HRC or a SPHL or some other suitable pressure vessel.[1]
- hyperbaric rescue vessel
A ship provided with equipment to handle the recovery of hyperbaric lifeboats and hyperbaric rescue capsules.[25]
- hypercapnia
Excessive level of carbon dioxide in the body, to a partial pressure of above 45 mmHg.[26]
- hyperfilter
Additional filter to produce air of oxygen compatible quality, usually for partial pressure gas blending. This may be built into the filling system or temporarily connected when required.
- hyperoxic linearity
Property of an oxygen sensor to produce linear output at partial pressures above the highest calibration point.[7][27]
- hyperventilation
- 1. A deliberate deep breathing to reduce blood carbon dioxide level to extend the duration of a free dive.
- 2. Rapid breathing as the body's response to hypercapnia.
- 3. Rapid, often shallow breathing, associated with panic.
- hyperventilation-induced blackout
- See: underwater blackout syndrome
- hypocapnia
Abnormally low tissue and blood carbon dioxide concentration.[28]
- hypothermia
A lowering of core body temperature, usually due to heat loss.[29]
- hypoxia
Abnormally low tissue oxygen concentration.[30] Insufficient oxygen in the body to support normal activities or consciousness.
- hypoxic training
- prolonged underwater distance swimming or extended breath-hold intervals.[31]
I
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- IAOGP
- ICD
- IDRCF
- IDRF
- International Diving Regulators and Certifiers Forum, previously International Diving Regulators Forum. A voluntary group of diving regulators and certifying agencies formed to work together toward mutual recognition and to identify and implement best practices in diver training with the object of harmonizing cross border diver training standards outside Europe. Members include Australia, Canada, France, Norway, South Africa and United Kingdom.[32]
- IDSA
- International Diving Schools Association: Formed with the primary purpose of developing common international diving standards for all occupational divers, Offshore, Inshore and Inland, and specialist related non-diving qualifications e.g. Supervisor, DMT and LST.[33]
- IMCA
International trade association for the marine contracting industry.
- inert gas
A gas which is not metabolically active, used to dilute the breathing gas.
- ingassing
Inert gas uptake in body tissues during a dive or other hyperbaric exposure.
- inherent unsaturation
Metabolic reduction of total gas pressure in the tissues . [34]
- inshore
- 1. Legal: Within the territory of a country in which national legislation applies. (e.g. for occupational health and safety). Generally within the 12 nautical mile limit. (as opposed to "offshore")
- 2. Oceanographic: (also 'nearshore) the region of the shoreface, where waves are affected by the seabed.[35]
- inshore diver
- Colloquial term for a diver who works on inland dive sites or coastal waters not associated with the oil and gas industry. Also referred to as "civils" as much of this work is connected with civil engineering works.[36]
- integrated open-circuit regulator
- integrated weight system
Any system for carrying dive weights on the buoyancy compensator or diving safety harness, avoiding the use of a separate weight harness or weightbelt.
- internal condition of cylinder
- The state of the internal surface of a cylinder regarding corrosion, contamination and cracking.
- International Association of Oil and Gas Producers
The international forum of the oil and gas producing industry.
- interstitial emphysema
- Gas trapped in the spaces between organs after lung barotrauma.
- inverter line
- in-water recompression
Recompression of a diver by returning to a specified depth in the water, followed by decompression on a specified gas, commonly oxygen, as treatment for decompression sickness or as prophylaxis for incomplete or missed decompression after a dive.
- IP
- Intermediate Pressure, or Interstage Pressure. The reduced pressure between the first and second stages of a diving regulator. Also referred to as LP (Low Pressure) in this context.
- isobaric blackout
- isobaric counterdiffusion
The diffusion of gases in opposite directions caused by a change in the composition of the external ambient gas or breathing gas without change in the ambient pressure.[37]
- isolation manifold
Connection between two scuba cylinders which when open allows free flow of gas in both directions between the cylinders, but has an isolation valve which can be used to block this flow.
- isolation valve
Valve in an isolation manifold (q.v.) used to close the gas passage through the manifold and isolate the contents of the two cylinders. Used to prevent a leak on one cylinder from causing the other cylinder to also lose gas.
J
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Contents: Top |
Subsection: Top, Ja, Je, Ji, Jo, Ju
Ja
- jackstay
A line secured at both ends to serve as a support[38] or guide.[39]
- jackstay search
Underwater search techniques using one or more jackstays to guide the searcher.[39]
- jack-up rig
A type of mobile platform that consists of a buoyant hull fitted with three or more movable legs, capable of raising its hull over the surface of sea. The buoyant hull enables transportation of the unit and all attached machinery to a desired location. Once on location the hull is raised to the required elevation above the sea surface on its legs supported by the sea bed.[40][41]
- J-cylinder
- Bulk gas storage cylinder with internal volume of about 50 litres.
Subsection: Top, Ja, Je, Ji, Jo, Ju
Je
- Jersey upline
Subsection: Top, Ja, Je, Ji, Jo, Ju
Ji
- JIC fitting
A type of pipe and hose fitting with a 37-degree flare seating surface. Commonly used in umbilical hose connections.[42]
- JIM suit
An atmospheric diving suit manufactured by Underwater Marine Equipment Limited.[43]
Subsection: Top, Ja, Je, Ji, Jo, Ju
Jo
- jocking strap
- jocking harness
- webbing strap system used with diving helmets to hold the helmet assembly down on the diver to prevent buoyancy lifting it when underwater.[44][45]
- Jonline
A short line used to connect to a shotline or anchor line, allowing the diver to move a short horizontal distance away to decompress. The line helps compensate for vertical movement in the anchor line or shot line due to waves.[46]
- job safety analysis
- JSA
A procedure to integrate health and safety principles and practices into a particular task or job. Each basic step of the job is analysed to identify potential hazards and controls for each hazard.[47]
- J-search
A variation on the movable jackstay search suitable for a single diver.
Subsection: Top, Ja, Je, Ji, Jo, Ju
Ju
- jump
A path from a main guideline to another which is not in contact[48]
- jump camera
- A camera mounted on a frame, which when lowered to the bottom of a body of water, takes a photograph, usually of the bottom under the camera. The frame constrains the camera to a fixed camera to subject distance, resulting in photographs of uniformly sized areas of bottom, equivalent to quadrats.
- Jump jacket
- A harness with integral buoyancy jacket specifically designed for commercial diving work with helmets and bells.[49]
- jump line
A short cave line, usually stored on a spool, used to connect between two permanent lines that are not in contact. May also be used to search for the other end of a break in a cave line and repair the break[48]
- jump reel
- jump spool
- A reel or spool with a relatively short line intended to be used as a jump line (q.v.).[50]
- J-valve
Scuba cylinder valve with lever operated reserve mechanism.[51]
Subsection: Top, Ja, Je, Ji, Jo, Ju