Scuba Dictionary

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.

Alveoli

Microscopic air sacs in the lungs where gas exchange occurs with the circulatory system.

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.

Anoxia

Absence of oxygen in the circulating blood or in the tissues.

Aorta

The largest vessel of the systemic arterial system, from which the main arteries carrying oxygenated blood branch and subdivide into smaller and smaller vessels.

Aqua-Lung

A scuba diving equipment manufacturer, formerly known as U.S. Divers.

Arteriole

Small artery.

Atrium

Chamber of the heart which provides access to another chamber called the ventricle.

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).

Helicopter Turns

A finning technique used by cave, wreck, and technical divers that allows them to make an easy turn using kicks alone. The technique is popular because it limits “silt outs” and helps a diver turn in a restricted environment.

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.

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.