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".
Air Embolism
Same as Arterial Gas Embolism
Air
Earth's atmospheric gas (our normal breathing gas) containing 21% Oxygen, 78% Nitrogen and 1% Argon
ATA
Atmospheres Absolute - absolute pressure measured in standard atmospheres (1013 mbar = 1 Ata)
Actual Bottom Time (ABT)
The bottom time computed from the beginning of the descent to the beginning of the ascent to the surface.
Alpha Flag
International Maritime warning flag for diver location. The flag indicates a diver is nearby underwater.
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.
Aqua-Lung
A scuba diving equipment manufacturer, formerly known as U.S. Divers.
Back Roll
A type of boat entry where the diver sits on the edge of the boat and leans back, falling into the water.
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.
BC or BCD
Buoyancy Compensator or Buoyancy Compensation Device
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).
Bounce dive
A dive that is performed only to reach a certain depth and then ascend immediately.
Bottle
Gas cylinder or scuba tank.
Bent
Indicates someone who experiences decompression sickness (DCS) symptoms.
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.
Blue water
Extremely clear water with distant visibility - as opposed to low visibility green water.
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.
C-card
Scuba diving certification card from scuba certifying agencies such as NAUI, BSAC, PADI, etc..
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.
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.
CNS Oxygen Toxicity
Central Nervous System Oxygen Toxicity
DCI or DCS
Decompression Illness or Decompression Sickness - "the bends"
Deco
Decompression. Usually refers to time at the end of the dive dedicated to off-gassing excess inert gases suchas nitrogen and helium. Can refer to any equipment used in decompression, i.e., deco mix, deco tanks, deco time, deco tables, etc.
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.
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.
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.
DPV
Diver Propulsion Vehicle. A battery powered underwater scooter that pulls divers through the water.
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.
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.
Dry suit
A water-tight 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 65°F.
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.
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.
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.
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).
Fsw
Feet of sea water - it indicates the ambient absolute pressure in sea water at the given depth.
Free diving
Also known as skin diving or breath hold diving without an underwater breathing aid.
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.
Genesis
A scuba diving equipment manufacturer. Manufacturer of isolation manifolds for scuba tanks.
GPS
Global Positioning System - a satillite system that allows users to obtain their precise location.
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.
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.
Hang tank
A scuba tank and regulator that is placed before the dive so it can be used during decompression.
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).
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.
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.
Hit
An occurrence of a DCS symptom.
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.
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 ank. 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.
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.
HP
Abreviation for "high-pressure".
Hydro
Hydrostatic testing of a scuba tank performed to verify tank integrity.
Hypercapnia
A higher than normal level of carbon dioxide (CO2) in the blood. Also hypercarbia.
Hypertension
A human condition where the blood pressure (gauge) is above 140/90.
Hypothermia
A body temperature colder than normal (37°C/98.6°F) that results from diving without adequate wetsuit or drysuit thermal insulation in cold water. Severe problems start to manifest when body temperature reaches about 35°C (95°F). Divers stop shivering at the onset of hypothermia.
IANTD
A scuba diving certification and instruction agency, International Association of Nitrox and Technical Divers.
IP
Abbreviation for "intermediate pressure" - the pressure at the output of your scuba regulator's 1st stage and input to the 2nd stage.
Isolation manifold
A tube that connects the high-pressure air from two tanks together and provides a valve to block the connection if desired.
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.
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.
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 bio-degrade. 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.
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.
Kit
A set of diving equipment (British).
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.
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.
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.
MARES
A scuba diving equipment manufacturer.
Mix
A combination of two or more gases in % different than air, either Nitrox, Heliox, Trimix or other mixture.
MOD
Maximum Operating Depth for a mixture of gases at a prescribed partial pressure of Oxygen to prevent Oxygen toxicity.
NACD
A scuba diving certifying and instruction agency, National Association for Cave Diving
NAUI
A scuba diving certifying and instruction agency, National Association of Underwater Instructors
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.
NSS-CDS
A scuba diving certifying and instruction agency, National Speleological Society - Cave Diving Section
Nitrox
Any mixture of oxygen and nitrogen. Generally, the oxygen % is greater than that of air, 21%.
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.
OMS
A scuba equipment manufacturer, Ocean Management Systems , that is known for supplying technical diving equipment.
OW
Refers to entry level PADI 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).
PADI
A scuba diving certifying an instruction agency, Professional Association of Diving Instructors. The largest scuba diving certification agency in the world.
PDIC
A scuba diving certifying an instruction agency, Professional Dive Instructors Corporation
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.
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.
PP
Abbreviation for "partial pressure"
psi
A pressure measurement unit, pounds per square inch.
Poseidon
A scuba equipment manufacturer based in Sweden.
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.
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 ??. Residual nitrogen time is always taken into consideration in determining the safe duration for any repetitive dive.
Scooter
An underwater Diver Propulsion Device, see DPV
SCUBA
Self-Contained Underwater Breathing Apparatus - normally refers to open-circuit scuba, where exhaled gas is vented and bubbles to the surface.
Second
Second stage regulator (octo)
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.
Silt
Fine sand or dirt accumulation underwater; so fine that when stirred, it makes a fog in the water that you cannot see through.
Silt-out
A condition where visibility is dropped to zero when divers kick up silt and contaminate the water.
SPG
Submersible Pressure Gauge - used underwater to determine the gas pressure remaining in a scuba tank.
SMB
A surface marker buoy - used to warn boaters to stay away so divers can safely surface.
Square dive
A dive profile where the bottom depth is constant from beginning to end.
Surface interval
The length of time spent on the surface, usually out of the water, between two consecutive dives.
Surf
The increased action of waves against the coastline or intertidal area; characterized by exceedingly active water motion, crashing against rocks or other objects in shallow water.
Tank
A SCUBA breathing gas cylinder.
Thermocline
A clearly defined depth where warmer and cooler water meet abruptly.
Tox
A slang term for "Central Nervous System Oxygen Toxicity".
Trimix
A gas mixture of three gases: Helium, Oxygen and Nitrogen