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A B C D E F G H I J K L M N O R S T

A
Arterial Gas Embolism - AGE

If you hold your breath and surface, you can damage your lungs and an AGE will result. This causes gas bubbles from the lungs to enter the blood stream by way of a burst alveoli. The bubbles can block blood flow to critical parts of the body, usually the brain or heart. This is one of the more common ways divers die, and why the most important rule in scuba diving is to "never hold your breath". (Back to Top)

Air Embolism

Same as Arterial Gas Embolism (Back to Top)

Air

Earth's atmospheric gas (our normal breathing gas) containing 21% Oxygen, 78% Nitrogen and 1% Argon (Back to Top)

ATA

Atmospheres Absolute - absolute pressure measured in standard atmospheres (1013 mbar = 1 Ata) (Back to Top)

Actual Bottom Time (ABT)

The bottom time computed from the beginning of the descent to the beginning of the ascent to the surface. (Back to Top)

Alpha Flag

International Maritime warning flag for diver location. The flag indicates a diver is nearby underwater. (Back to Top)

Alpha Flag

Ambient Pressure

The pressure surrounding you. On land, it results from the weight of the atmosphere. At depth, it comes from the weight of the water plus the weight of the atmosphere. (Back to Top)

Aqua-Lung

A scuba diving equipment manufacturer, formerly known as U.S. Divers. (Back to Top)

Aqua Lung Logo

B
Back Roll

A type of boat entry where the diver sits on the edge of the boat and leans back, falling into the water. (Back to Top)

Bailout Bottle

A cylinder of gas carried by hard-hat divers or Rebreather divers to be used to get to the surface if their main gas supply equipment equipment fails. (Back to Top)

Bailout Bottle

BC or BCD

Buoyancy Compensator or Buoyancy Compensation Device (Back to Top)

Zeagle Ranger BC

Bottom mix

Refers to the ratio of gases in a diver's main tank planned for use at the deepest depth of the dive. Mix ration is usually given by two numbers referring to Oxygen % and Helium %, for example, 11/50 for 11% Oxygen, 50% helium and remainder (39%) Nitrogen. The term may also refer to the tank(s) containing the bottom mix, or the actual gas itself inside the tank(s). (Back to Top)

Bounce dive

A dive that is performed only to reach a certain depth and then ascend immediately. (Back to Top)

Bottle

Gas cylinder or scuba tank. (Back to Top)

Tanks

Bent

Indicates someone who experiences decompression sickness (DCS) symptoms. (Back to Top)

Barotrauma

Physical injury caused by effects of pressure underwater. Includes all types of such injuries such as arterial gas embolism, DCS, vertigo/inner ear problems, and burst eardrum. (Back to Top)

Blue water

Extremely clear water with distant visibility - as opposed to low visibility green water. (Back to Top)

C
CESA Controlled Emergency Swimming Ascent

Out-of-air option when you've strayed too far away from your alternate air source, and are above 40 fsw. (Back to Top)

C-card

Scuba diving certification card from scuba certifying agencies such as NAUI, BSAC, PADI, etc.. (Back to Top)

C Card

Carbon Monoxide

Chemical symbol "CO". The gas is odorless, tasteless, highly poisonous gas given off by incomplete combustion of hydrocarbon fuels. It prevents Hemoglobin in human blood from distributing oxygen throughout the body. Results in cherry-red lips and nail beds in victims breathing small amounts of this gas. (Back to Top)

Compartment

A theoretical representation of body tissues with an arbitrarily assigned half time for nitrogen uptake and elimination. In designing decompression tables the body's various tissues are grouped into a finite number of compartments for purposes of making calculations, e.g., five, six or more. (Back to Top)

CNS Oxygen Toxicity

Central Nervous System Oxygen Toxicity (Back to Top)

D
DCI or DCS

Decompression Illness or Decompression Sickness - "the bends" (Back to Top)

Deco

Decompression. Usually refers to time at the end of the dive dedicated to off-gassing excess inert gases such as nitrogen and helium. Can refer to any equipment used in decompression, i.e., deco mix, deco tanks, deco time, deco tables, etc. (Back to Top)

Decompression dive

Any dive where the diver is exposed to a higher pressure than when the dive began; the decompression occurs as the diver ascends. Technically, every dive is a decompression dive. But the term, "decompression dive", normally refers to a dive that requires "special" time for decompression at the end of a dive. (Back to Top)

Decompression schedule

A specific decompression procedure for a given dive profile, normally indicated as depth/minutes. The schedule can be computer generated or obtained from Tables such as the US Navy Decompression Tables. (Back to Top)

DIN valve

An extremely reliable tank valve and regulator fitting which encloses the O-ring so it cannot "burst" as commonly occurs with Yoke valves. (Back to Top)

DIN Valve

DPV

Diver Propulsion Vehicle. A battery powered underwater scooter that pulls divers through the water (Back to Top)

D-ring

A "D" shaped stainless steel ring located on the BC straps or scuba tank that is used to make reliable connections with other equipment. (Back to Top)

D Ring

Doubles

Two tanks connected together in a backpack, usually identical "twin" tanks connected by a manifold so the air supplies are common. Can be independent doubles, which have no manifold, and tanks may not be identical. (Back to Top)

Nitrox Doubles

Dry suit

A watertight garment that keeps the diver's body warm by providing insulation with a layer of gas, such as air. It is used for diving in waters that are too cold for comfortable wet suit protection, usually below 65F. (Back to Top)

DUI TLS 350

E
EAD

Equivalent Air Depth. Calculated when using Nitrox at a given % Oxygen and using Air Tables for Decompression Planning. the EAD for Nitrox in the 21 - 50% range is always less than the actual depth. (Back to Top)

EANx

Enriched Air Nitrox - Breathing gas with increased % of Oxygen, greater than 21% in normal air. Requires special training before use. Allows longer bottom times at limited depths. Read more on our Nitrox Page.
(Back to Top)

Nitrox Tank

END

Equivalent Nitrogen Depth, or Equivalent Narcotic Depth. Used by Nitrox and Trimix divers. The (different) depth at which air would cause as much narcotic effect as the gas you are using at maximum depth. For a 14/33 trimix (helium-air), the END is 180 feet where the MOD (maximum operating depth) is 297 feet @ 1.4 ppO2. (Back to Top)

Eustachian tube

A short, cartilaginous tube connecting the back of the nose to the middle ear. The anatomy of this tube is such that it tends to close naturally when ambient pressure is higher than middle ear pressure (as on descent in a dive), and tends to open naturally when ambient pressure is lower than middle ear pressure (on ascent). (Back to Top)

Middle Ear

F
Fsw

Feet of sea water - it indicates the ambient absolute pressure in sea water at the given depth. (Back to Top)

Free diving

Also known as skin diving or breath hold diving without an underwater breathing aid. (Back to Top)

G
Goodman handle

A handle for an underwater torch that fits over your hand. It allows you to point the torch by moving your arm and still keeps your hand free for doing other things. (Back to Top)

Goodman Handle

Genesis

A scuba diving equipment manufacturer. Manufacturer of isolation manifolds for scuba tanks. (Back to Top)

Genesis Logo

GPS

Global Positioning System - a satellite system that allows users to obtain their precise location. (Back to Top)

H
H-Valve

A tank Valve with two outlets for two regulator 1st stages. There are really two valves with one tank connection. This allows you to turn off one valve if that regulator free-flows, and still be able to use the rest of the air in the tank. An H-valve is designed so that it can be used to make a manifold by removing one of the valves and adding the interconnecting tube. (Back to Top)

H Valve

Hang time

Time spent hanging from a rope, decompressing. To perform a decompression stop at one depth or a decompression profile of a series of depths. (Back to Top)

Hang Time

Hang tank

A scuba tank and regulator that is placed before the dive so it can be used during decompression. (Back to Top)

Haldane Theory

Diver Decompression theory that nitrogen gas is absorbed and given off in exponential fashion during a dive, and that there is a safe ratio of pressure change for ascent (originally, 2:1, but lowered and changed later for various tissue pressure groups). (Back to Top)

Heliox

A gas mixture containing two gases, Oxygen and Helium, used for deep diving to remove the narcotic effect of nitrogen, but subject to HPNS at depths near 400 fsw. (Back to Top)

HPNS

Abbreviation for " High Pressure Nervous Syndrome ". A condition that occurs when using inert gasses at or below 400 fsw and is also related to the rate of change in pressure. Decent rates of greater than 1 ft per minute can cause onset of the condition near this depth. The condition is most severe when the breathing gas is Heliox, with Trimix symptoms being experienced near 600 fsw. The symptoms include muscle twitching, dizziness, nausea, vomiting, postural and intention tremors, fatigue and somnolence, stomach cramps, and general loss of body control. The addition of small amounts of Nitrogen (up to 10%) to a Heliox mix are known to abate HPNS. (Back to Top)

Hit

An occurrence of a DCS symptom. (Back to Top)

Hogarthian system

The "Do it Right" (DIR) system started by William Hogarth Main that was based in cave diving but has now been promoted in all types of technical diving by the WKPP and GUE. (Back to Top)

Hookah

A method of shallow scuba diving that supplies air from the surface through a long hose. Usually consists of a gas powered air compressor on a floating platform with long hoses reaching down to divers having a second stage only for breathing. The depth limit of these systems is around 30 feet. Divers have weight belts and BCs, but no tank. For certain shallow areas, this type of diving has distinct advantages, in that you can dive a very long time without surfacing for additional air, and there is no hindrance of a scuba tank on your back. However, you must pull the floating hookah along with you by the hose. (Back to Top)

Hookah System

Horse collar

A term that describes the initial models of buoyancy control devices because they looked like the horse collar used when horses were used to pull loads such as a wagon or buggy. Some old die-hard divers still use these. Many of them are orally inflated and have CO2 cartridges for emergency air inflation, as was popular 20 - 30 years ago. Many feel that these cartridges are unsafe and prone to accidental triggering. It is also more convenient and safer to have a push-button inflator as in modern BCs. Snorkelers may now obtain a similar device that is inflated orally. (Back to Top)

Horse Collar

HP

Abbreviation for "high-pressure". (Back to Top)

Hydro

Hydrostatic testing of a scuba tank performed to verify tank integrity. (Back to Top)

Hypercapnia

A higher than normal level of carbon dioxide (CO2) in the blood. Also hypercarbia. (Back to Top)

Hypertension

A human condition where the blood pressure (gauge) is above 140/90. (Back to Top)

Hypothermia

A body temperature colder than normal (37C/98.6F) that results from diving without adequate wet suit or dry suit thermal insulation in cold water. Severe problems start to manifest when body temperature reaches about 35C (95F). Divers stop shivering at the onset of hypothermia. (Back to Top)

I
IANTD

A scuba diving certification and instruction agency, International Association of Nitrox and Technical Divers. (Back to Top)

IANTD

IP

Abbreviation for "intermediate pressure" - the pressure at the output of your scuba regulator's 1st stage and input to the 2nd stage. (Back to Top)

Isolation manifold

A tube that connects the high-pressure air from two tanks together and provides a valve to block the connection if desired. (Back to Top)

Isolation Bar

J
Jon line

A short line used to attach yourself to the anchor line at an offset distance. This allows several divers to perform deco stops at the same depth comfortably, and remain in contact with the anchor line. Used in medium to strong current or when there are other divers performing deco below - the offset distance prevents the other divers' air bubbles from becoming a nuisance. Named for the first user / originator, Jon Hulbert. (Back to Top)

Jon Line

J-valve

Also called a "reserve" valve. An outdated type of scuba tank valve that shuts off the air supply when air pressure drops to 400 - 700 psi. It then allows the use of the remaining air if the "reserve" lever on the valve is pulled down. This type of valve was used before submersible pressure gauges (SPGs) were standard scuba equipment. Now, the J-valve is a source of accidents when the user is unaware of it and the air suddenly is shut off. Users of tanks with J-valves should always make sure that the lever is in the down position before diving using a normal SPG. (Back to Top)

J Valve

 

Jersey Reel

A large spool of rope used to provide a decompression line in case of emergency or in a contingency when divers choose or are prevented from returning to the anchor line for open water ascent. The reel uses 1/4 inch sisal line that will eventually biodegrade. The divers use the spool to float a lift bag and then attach the rope to a stable object such as the wreck frame or large rock on the bottom. (Back to Top)

K
K-valve

A normal scuba tank valve that allows simple on-off control of the air supply. It may have either DIN or Yoke fitting. (Back to Top)

K Valve

Kit

A set of diving equipment (British) (Back to Top)

L
Lift bag

An underwater air sack with a connecting rope that, when air is added from a diver's regulator, pulls upward on the rope and allows divers to lift heavy items from the bottom. (Back to Top)

Lift Bag

LP

Abbreviation for "low-pressure". The term is used generally the same as "intermediate pressure" (IP) when discussing scuba regulators. Often refers to the "low-pressure" LP hose connecting the regulator 1st stage LP or IP port to the BCD inflator. (Back to Top)

M
Manifold

A tube that connects the high-pressure air from two tanks together so that the air from both tanks may be used from either regulator on the tanks. (Back to Top)

Dual Manifold

Mares

A scuba diving equipment manufacturer. (Back to Top)

Mares Logo

Mix

A combination of two or more gases in % different than air, either Nitrox, Heliox, Trimix or other mixture. (Back to Top)

MOD

Maximum Operating Depth for a mixture of gases at a prescribed partial pressure of Oxygen to prevent Oxygen toxicity. (Back to Top)

N
NACD

A scuba diving certifying and instruction agency, National Association for Cave Diving. (Back to Top)

NACD

NAUI

A scuba diving certifying and instruction agency, National Association of Underwater Instructors (Back to Top)

NAUI Logo

NDL

Abbreviation for "No-Decompression Limit". Ideally, the maximum bottom time at a given depth for which no decompression stop is required. However, safe divers always perform a safety stop when diving to the limit. (Back to Top)

NSS-CDS

A scuba diving certifying and instruction agency, National Speleological Society (Back to Top)

NSS/CDS Logo

Nitrox

Any mixture of oxygen and nitrogen. Generally, the oxygen % is greater than that of air, 21%. (Back to Top)

Nitrox Sticker

O
Octo

A backup second stage regulator connected to your 1st stage, intended for the benefit of other divers in case their air supply should fail. It is the alternate air source that forms the basis for the "buddy" system. (Back to Top)

Poseidon Octo

OMS

A scuba equipment manufacturer, Ocean Management Systems , that is known for supplying technical diving equipment. (Back to Top)

OMS Logo

OW

Refers to entry level scuba diving certification, Open Water Diver. Open water divers may not dive in overhead environments that restrict direct ascent to the surface (not open water). (Back to Top)

P
PADI

A scuba diving certifying an instruction agency, Professional Association of Diving Instructors. The largest scuba diving certification agency in the world. (Back to Top)

PADI Logo

Patent Foramen Ovale

(PFO - abbreviated). A medical condition that makes DCS more likely in divers who have it. A flap between the two large chambers of the heart that can open under certain conditions and allow blood to recirculate back through the body without returning first to the lungs. Small bubbles in this blood are not filtered out by the lungs as they usually are, making DCS more likely. A significant number of divers have this condition. (Back to Top)

Pony bottle

A reliable alternate air source for self-sufficient divers. A smaller but independent air supply to be used in case of main air failure. Consists of a small scuba tank with a regulator attached. The capacity of these tanks is usually 13 to 30 cubic feet. (Back to Top)

Pony Bottle

PP

Abbreviation for "partial pressure" (Back to Top)

psi

A pressure measurement unit, pounds per square inch. (Back to Top)

Poseidon

A scuba equipment manufacturer based in Sweden. (Back to Top)

Poseidon Logo

 

R
Rule of Thirds

A proven gas conservation guideline and safety procedure, generally used by cave divers and wreck penetration divers, but also used by deep divers. The rule is used often by divers using doubles without a pony. The rule is:

  • Use the first third of total gas pressure to get where you're going and begin the return trip.
  • Use second third of total gas pressure to return to the entry/surface.
  • Save the last third for unforeseeable problems. The last gas third might be needed by another diver who is low on gas, in case you lose some gas due to a regulator free-flow, or your gas consumption rate is higher than expected. (Back to Top)

RNT

Abbreviation for "Residual Nitrogen Time". Residual Nitrogen Time - the time it would take to off-gas any extra nitrogen remaining after a dive; in dive tables, RNT is normally designated by a letter A through L. Residual nitrogen time is always taken into consideration in determining the safe duration for any repetitive dive. (Back to Top)

S
Scooter

An underwater Diver Propulsion Device, see DPV. (Back to Top)

Dive Scooter

SCUBA

Self-contained Underwater Breathing Apparatus - normally refers to open-circuit scuba, where exhaled gas is vented and bubbles to the surface. (Back to Top)

Second

Second stage regulator. See Octopus. (Back to Top)

Spare death

A negative reference to the small alternate air source marketed as "Spare Air", because many feel it does not have enough air to be useful in an out-of-air emergency. (Back to Top)

Spair Air

Silt

Fine sand or dirt accumulation underwater; so fine that when stirred, it makes a fog in the water that you cannot see through. (Back to Top)

Silt-out

A condition where visibility is dropped to zero when divers kick up silt and contaminate the water. (Back to Top)

SPG

Submersible Pressure Gauge - used underwater to determine the gas pressure remaining in a scuba tank. (Back to Top)

SPG

SMB

A surface marker buoy - used to warn boaters to stay away so divers can safely surface. (Back to Top)

Surface Marker Buoy

Square dive

A dive profile where the bottom depth is constant from beginning to end. (Back to Top)

Surface interval

The length of time spent on the surface, usually out of the water, between two consecutive dives. (Back to Top)

Surf

The increased action of waves against the coastline or inter tidal area; characterized by exceedingly active water motion, crashing against rocks or other objects in shallow water. (Back to Top)

T
Tank

A SCUBA breathing gas cylinder. (Back to Top)

Thermocline

A clearly defined depth where warmer and cooler water meet abruptly. (Back to Top)

Tox

A slang term for "Central Nervous System Oxygen Toxicity". (Back to Top)

Trimix

A gas mixture of three gases: Helium, Oxygen and Nitrox (Back to Top)

Trimix Sticker

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