Scuba Diving Glossary and Terms

An alphabetical list of terms used in scuba diving.

  • Absolute pressure: The equivalent of atmospheric pressure plus gauge pressure calculated by using perfect vacuum as the 0 point.
  • Acetal resin: Very strong, high performance polymer used to replace lightweight metal.
  • Air: Gas mixture comprised of 21 percent oxygen, 78 percent nitrogen, and 1 percent other gases that when compressed becomes breathable air used for scuba diving.
  • Air compressor: A piece of scuba diving equipment that compresses or pressurizes air.
  • Air tank: Cylinder of compressed air used for scuba diving.
  • Alternate air source: Secondary or backup regulator used in place of the primary regulator in emergency cases.
  • Ambient light: Natural underwater sunlight.
  • Ambient pressure: Surrounding pressure on land from the weight of the atmosphere. Underwater, ambient pressure is the pressure that occurs from the surrounding water.
  • Analog device: Pressure gauge involving a needle moving around a dial used for dive tanks.
  • Argon: Gas that makes up about one percent of air.
  • Ascent/descent line: Surface line that controls a diver's rater of ascent and descent into the water.
  • Atmospheric pressure: Pressure of the weight of the atmosphere.
  • Artificial spit: Scuba mask defogging liquid.
  • Ascent bottle: Extra cylinder of air used for decompression stops during deep diving.
  • Axial flow scrubber: Scrubber canister used in re-breathers where exhaust enters one end and exits the other.
  • Back gas: Breathing gas contained in cylinders carried on a diver's back.
  • Bail-out bottle: Tank containing backup air to be used only in cases of emergency.
  • Bar: Term used in measuring atmospheric pressure. One bar equals 15 lbs of atmospheric pressure per Basic cave training: Training that covers the basics of cave diving.
  • The bends: Term used to denote decompression sickness.
  • Bladder: Container of air inside of buoyancy compensator that balances buoyancy levels.
  • Booties (scuba booties): Neoprene socks worn by scuba divers.
  • Bottom time: Length of time a diver is underwater.
  • Bottom timer: Depth timing device that automatically starts when the diver begins descending.
  • Breathing loop: Part of a re-breathing system comprised of a mouthpiece, inhalation and exhalation bags, hoses, and canister.
  • Buddy bottle: Independent bottle carried by a diver in the place of dive buddy in cases of emergency.
  • Buoyancy: Upward force exerted on something in water.
  • Buoyancy compensator: Inflatable vest worn by the diver to help control buoyancy.
  • Buoyancy control device: Device that aids a diver in maintaining proper buoyancy.
  • Burst disk: Copper disk designed to break when tank pressure is exceeded.
  • Boots: Foot protection on land or in water, usually made of neoprene.
  • Bypass valve: Manual valve that lets gas into the breathing loop of a re-breather.
  • Cage: Acronym for "cerebral arterial gas embolism".
  • Canister light: Large, long-burning light attached to a battery pack contained in a canister used for scuba diving.
  • C-card: A diver's certification card.
  • Caustic cocktail: Very dangerous mixture of water and hydroxide chemicals caused by water flooding the scrubber canister.
  • Cave diving: Highly specialized diving requiring special training and equipment due to the fact that it involves an overhead environment preventing a diver from making a direct descent into the water.
  • Certification dive: Open water dives that a diving trainee performs after completing their academics and pool work.
  • Check-out dive: A dive that demonstrates diver possesses the necessary skills required for a dive.
  • Check valve: Re-breather valve that ensures that gas or fluid only flows in one direction.
  • Closed circuit scuba: Noiseless and bubble-less, a circuit allowing divers to re-breath exhaled air by removing the C02 and replacing it with 02.
  • Compressed air: Air that is kept under a certain pressure in order to be used as a source of breathing air for scuba diving.
  • Counter lung: The breathing bag component of the re-breather system.
  • Cylinder: Scuba tank containing breathable gas.
  • Deco: Short for decompression
  • Decompression: Reducing ambient pressure resulting in reduced gas pressure within the body.
  • Decompression sickness: Illness that occurs when ambient pressure is reduced and nitrogen leaves the body.
  • Decompression stop: Also called a safety stop, a set time and depth of a diver to eliminate inert gasses in order to avoid decompression sickness.
  • Deep diving: Refers to either recreational diving up to 60 feet, or technical diving up to 130 feet.
  • Deep stops: Stopping to note physical symptoms after completing several deep dives in order to help stabilize gas tension for the ascent.
  • Demand valve: Part of the diving regulator that delivers gas to the mouth.
  • Depth gauge: Measures the depth of a diver.
  • Dive computer: Electronic device that measures inert gas pressure levels, depth, time, ascent rates, warns diver about decompression stops, and more.
  • Dedicated dive resort: A resort designated for recreational scuba diving.
  • Dive skin: Full body suit made of a thin piece of material, usually Lycra, to protect the diver from scrapes and stings.
  • Dive buddy: Underwater diving partner.
  • Diving weights: Weights worn by diver to offset body buoyancy.
  • Doubles: Two cylinders banded together for extended dives.
  • Drift diving: Diving with the current, as opposed to anchor diving.
  • Dry suit: water proof, water tight insulating garment to help keep the diver's body warm.
  • Duel regulator systems: Two regulators attached to a single air supply as an extra safety precaution.
  • Enriched air nitrox: Oxygen enriched breathing gas used instead of compressed air.
  • Exhaust valve: One-way valve in the exhaust hose to keep gas flowing in the right direction.
  • Exposure protection: Body suit worn by a diver to maintain body temperature and protect the body.
  • Fins: Equipment worn on the feet to help propel the body through the water while kicking the legs.
  • First stage regulator: Regulator attached to the scuba cylinder valve to stabilize tank pressure.
  • Flow meter: Device that shows the flow rate.
  • Flow restrictor: Restriction placed in a flow line, often used with low pressure hoses, to limit the volume of gas.
  • Gaiters: Wraps used to squeeze airspace from the lower legs of a wet suit to help maintain proper buoyancy.
  • Galvanic corrosion: Corrosion of two or more metals in contact with each other.
  • Galvanized: Metal preservation using rust resistant zinc coating on steel.
  • Gas analysis: Method to determine fractions of gas contained in a breathing mixture.
  • Gauge reader: A bifocal lens that helps a diver read a gauge.
  • Granny line: Also called a 'Jerry line'; a line running from the hang bar to the anchor line.
  • Gas saturation: Level of dissolved gas in body tissue reaches its maximum.
  • Halocline: Change in salt content in water not apparent to divers unless it creates buoyancy changes.
  • Hang tank: Extra tank containing deco mix used during the decompression stop.
  • Harness: Used to secure a back-plate to a diver.
  • Heliox: Combination helium and oxygen used for very deep diving.
  • Helium: A light gas used for very deep diving.
  • High pressure cylinder: Steel cylinders used at pressures of 3,500 csi.
  • Hogarthian: Named after Florida cave diver William Hogarth Main, a configuration based on lowering equipment to a minimum configuration to maximize gas efficiency.
  • Hookah: Surface-supplied breathing apparatus consisting of a cylinder and a long hose, used for shallow diving.
  • HP hose: High pressure hose attached to a first stage regulator and running to the air pressure gauge.
  • Hyperbaric chamber: Air tight chamber used for treating decompression sickness.
  • Independent doubles: Double cylinder diving without a manifold.
  • Inflator valve: Buoyancy compensator valve to which a second stage low pressure hose is attached.
  • J-valve: An older kind of cylinder valve that released reserves gas by way of a spring loaded part.
  • Jasper reel: Named after Florida diver Woody Jasper, a reel with a handle on the side instead of on top.
  • Jon line: Short line divers attach to anchor line used for decompression diving.
  • K valve: On/off cylinder valve.
  • Kit: British for diving equipment.
  • Lay line: In cave diving, the first line used in an unexplored cave site.
  • Lift bag: Bag divers use to lift underwater objects.
  • Lift capacity: Amount of buoyancy given by a buoyancy compensator.
  • Manifold: Piece of scuba equipment used for double cylinder systems.
  • Mask: Glass window in diving helmet allowing diver to see clearly underwater.
  • Mask squeeze: What occurs when a diver fails to equalize his or her mask before a rapid descent.
  • Mixed gas: Non-air mixture, or gas mixed with nitrogen.
  • MOD: Acronym for "maximum operating depth".
  • Mooring Buoy: Permanent marker for tying a dive boat to, often used to mark common dive areas.
  • Multilevel diving: Spending time in varying depths in a single dive.
  • Mushroom valve: Second stage exhaust valve.
  • Narcosis: Inert gas intoxication.
  • Nitrogen: Inert gas making up 78 percent of air.
  • Nitrogen narcosis: Intoxicating effect on a diver due to toxic levels of nitrogen in breathing gases.
  • Night diving: Scuba diving done at night, usually around dusk.
  • Nitrox: Mixture of nitrogen and oxygen.
  • O-ring: Common seal for scuba equipment.
  • Octopus: Used in place of a primary regulator during ascent.
  • Off gassing: Also called "out gassing", process of releasing inert gasses, such as nitrogen, at the surface.
  • Open circuit scuba: Breathing apparatus involving exhaling air into the water.
  • Open water certification: Four or five open water dives are performed upon completion of a scuba diving training course, after which the diver receives a certification card.
  • Open water diving: Recreational diving done in natural open waters with no overhead obstructions.
  • Oxygen toxicity: Illness resulting from breathing too much oxygen.
  • P-valve: Dry suit equipment allowing the diver to urinate during a dive.
  • Pony bottle: Small diving cylinder used in cases of emergency.
  • Purge valve: Allows mask and regulator to be cleared without having to remove them.
  • Re-breather: Scuba apparatus that recycles exhaled air and prepares the carbon dioxide for re-use.
  • Recreational scuba diving: Diving no deeper than 130 fsw using only compressed air and with no decompression stops.
  • Dive regulator (scuba regulator): One of the most critical pieces of scuba diving gear; supplies the diver with breathable gas at ambient pressures.
  • Rinse tank: Fresh water tank for rinsing dive equipment after use.
  • Rule of thirds: An air management rule whereby a diver uses a third of the tank to descend, a third to resurface, and the remaining third for a buddy in case of emergency.
  • Safety stop: Stopping for one to three minutes at the end of every dive in order to re-gas.
  • SCUBA: Acronym for "self-contained underwater breathing apparatus".
  • Scooter: Diving portal allowing a diver to navigate around objects underwater.
  • SCR: Short for 'semi-closed re-breather'.
  • Scrubber: Part of a re-breather system that recycles exhaled oxygen.
  • Side mount diving: Divers mount cylinders on the side to allow entry into narrow passages.
  • Singles: Single dive cylinders
  • Solo diving: Diving alone without a buddy: usually not recommended.
  • Stage bottle: Container of decompression gas used to extend dives and aid decompression.
  • Snorkel: Flexible tube used for breathing underwater and close the surface.
  • Surface interval: Amount of time spent on the surface between dives.
  • Table 6: Navy treatment for decompression sickness.
  • Tank: Slang for scuba cylinder
  • Technical diving: Descending to depths beyond those of common recreational diving.
  • Time to fly: It is recommended that a diver wait 24 hours after diving to fly in a plane in order to recover from the effects of decompression.
  • Trimix: Mixture of helium, oxygen, and nitrogen used for deep diving.
  • Upstream valve: Valve that works against, and not with, pressure.
  • V-weight: Weight carried between cylinders to normalize buoyancy.
  • Veering: Wind shifting into clockwise direction.
  • Vertigo: dizziness caused by inner ear problems.
  • Visibility ('vis'): How far a diver can see underwater.
  • Wall dive: Diving near an underwater cliff.
  • Wet suit: Diving suit that provides thermal and other protection from the elements.
  • Wing: Back-mounted buoyancy compensator used by cave and technical divers.
  • Wreck diving: Diving into natural and man-made disaster sites.
  • X scooter: Very lightweight diver propulsion vehicle.
  • Yaw: Swinging off course.
  • Y valve: A double outlet on a tank.

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