10l, 12l, 15l:
Refers to the size of air cylinders used in Europe, the number measures
in litres the capacity of the cylinder (this is technically known as the water capacity).
So an empty 15l cylinder contains 15 litres of air, double the air pressure (2 BAR)
and it contains 30 litres of air. In the US they use cubic feet of air, rather than litres.
The depth in metres. In the US they use feet.
Part of a Regulator, the central part that attaches to the diving cylinder.
Apart from serving as the cylinder attachment the 1st Stage is a pressure reducing
valve that reduces the cylinder pressure (200+ BAR at the start of a dive) to a lower
10 to 15 BAR pressure. There are ports (screw fittings) on the 1st stage that hoses
to feed other equipment attach to, there are normally four low pressure ports (LP Feed)
and two high pressure (HP Feed) ports.
The part of the regulator you breathe from, also known as a primary, octopus or demand valve.
A type of fitting for connecting the regulator 1st stage to the cylinder pillar
valve. The pillar valve is clamped into a frame on the regulator 1st stage, the
assembled item resembles the letter 'A'. The A-Clamp is the 'traditional' way of
connecting the 1st stage to a cylinder and is used throughout the world.
Alternative Air Source. A 'spare' secondary demand valve (often referred to as an octopus)
carried by a diver for their own use or their buddy's use should something go wrong with
their normal equipment. First brought into diving by cave divers and finally these
pieces of equipment are now an essential part of diving equipment.
Adjustable Buoyancy Life Jacket. An outdated style of BCD that is still used by
some divers. Looks like a standard 'over the head' life jacket (it is sometimes called a
horse collar) but the amount of air in it can't be controlled. Now replaced by the BCD or Wings.
The pressure currently acting on a divers body, as you read this
you should be experiencing an absolute pressure of 1 BAR, i.e Atmospheric pressure.
Each 10m of water above you adds 1 BAR, so a diver at 30m is at 4 BAR absolute pressure -
4 times the normal atmospheric pressure. When we breath at depth we breath at absolute
pressure (the demand valve makes sure of this), so at 30m (4 BAR) we use twice as much air
as at 10m (2 BAR).
Automatic Dilutant Valve
Full face mask, trade name (FFM)
Arterial Gas Embolism
Association of Independent Scuba Educators
Diver who sucks tank dry in record time
American Nitrox Divers Incorporated ANDI website
Advanced Open Water. A PADI Advanced diver qualification. Some people think
this is a course for "advanced divers", but it is a course for Advanced Diving techniques
for Open Water divers.
Absolute Pressure or Ambient Pressure
Ambient Pressure Diving (home of the Inspiration/Evolution, Yellow Turtle or YBOD!)
Atrial Septal Defect, 'Hole in Heart'
Australian Speleological Federation
American Sign Language
An inert gas sometimes used by divers to inflate their dry suits, argon is used
because it is a much better insulator from the cold than normal air (some say as much as 50% better).
Australian Underwater Federation
Auto Air/Air II:
Another form of AAS. A demand valve that is built into the
inflator/deflator control of a BCD.
Part of a different type of diving rig, rigid (normally stainless steel or aluminium)
that is designed to carry a twin set of cylinders. Used in conjunction with a wing BCD.
A measure of pressure, 1 bar = atmospheric pressure. The amount of air in a
cylinder is measured in BAR, it is typically about 220 BAR at the start of a dive and
50 BAR or more at the end.
A general term to describe a physical injury caused by a change in pressure.
Buoyancy Control Device. Normally the term used for the waistcoat like jacket
that divers wear to which most of their equipment is attached. The BCD contains a bag that
can be inflated and deflated, this controls the buoyancy of the diver.
The 'general public' term for what we call DCS or DCI. 'The Bends' is actually
a mild form of DCS where bubbles form in joints such as elbows, to relive the pain and
pressure people tend to continually bend their arms - hence the name 'The Bends'.
Backplate, also Blood Pressure
Beats Per Minute (heart/pulse rate)
The British Sub Aqua Club. An english diver training agency.
One part Tia Maria, one part Bailey's and one part Cointreau :-)
Heart beating too slow.
Viz so bad you had to feel your way through the dive
Used in technical diving, the two divers descend to about 6m and swim around their
buddy looking for bubbles (leaks) before the descent.
Your diving partner, we normally dive in twos - a buddy pair.
A pre-dive check where two divers check each others dive equipment
and explain how the essentials work and where they are located.
Keeping an eye on your buddy during a dive and checking that
everything is OK.
Whether something floats, sinks or hovers in the water.
Negative Buoyancy = sinking, Neutral Buoyancy = hovering, Positive Buoyancy = rising or
floating. Divers should be at (or near) neutral buoyancy at all times so that they are
in total control of where they are in the water, this is achieved by injecting air into or
dumping air from their dry suit or BCD.
Acronym used for your Buddy Check, stands for BCD, Weights, Releases, Air and Final ok.
A couple of ways to remember this is: Being Wary Reduces All Failures; Beer, Wine Rum Are Fine;
Big Women Really Are Fun; Big White Rabbits Are Fuzzy; Boogie With the Rich And Famous; Bruce Willis Ruins All Films
A (normally rock) tunnel with no immediate route up or out. Some underwater caves can go on for miles.
Cave diving is a very specialised form of diving requiring special training, equipment
and techniques. Without all three of these it is very
A depression in a rock face or the 'twilight zone' entrance to a cave.
A cavern constitutes an overhead environment but for a cavern you can clearly see the
light and the way out. When you reach the stage where you can't see the light any more you
are in a cave!
Closed Circuit Rebreather. A type of rebreather that uses oxygen sensors and
controls the level of oxygen being breathed. Makes very efficient use of gas and cuts
down the time needed for deco. With regular SCUBA (open circuit) the exhaled gases are released into the water,
whereas with a CCR the gases are recirculated and oxygen (or diluent) added as necessary according
to the diver's depth and gas requirements.
Short for decompression chamber. A medical facility where a diver can be
pressurised to simulate diving pressures. Used to treat DCS amongst other things.
A small piece of diving electronics worn on the wrist or included in the
console. It constantly displays information such as current depth, maximum depth, dive time
and remaining no stop time. It can calculate the decompression requirements for the dive.
Most divers carry a dive computer. Some are quite basic "bottom timers", but you can choose
some different models that show you your ascent rate, Oxygen Toxicity levels, even cylinder pressure.
The higher end (i.e. more expensive) computers let you programme in different gasses to use and you
can switch between them during the dive. Some even have games on them to use during your decompression stop!
Part of a regulator, contains some of the instruments used by a diver.
Typically there is a pressure gauge showing how much air is left in the cylinder, a depth
gauge to show how deep you are and a compass to navigate with. The console attaches to one
of the HP Feeds of the 1st Stage.
Cylinder (AKA tank\bottle):
A steel or aluminium bottle or tank containing our breathing (normally...)
gas. They come in various sizes up to 20l and two pressure ratings, the standard 232 BAR
and 300 BAR. They can also be made of carbon fiber, but these are a lot more expensive.
Closed Circuit Rebreather
Cave Diving Group
Counterlung (on rebreathers)
Decompression Sickness, the modern term for a whole host of very nasty things
(the 'bends' is one minor form of DCS) that can happen if you break the rules or things go
badly wrong. Sometimes even if you follow all the rules, you may still get a mild dose of DCS.
During a dive nitrogen is forced into a divers body due to the pressure, when returning to
the surface this nitrogen disperses again. If this happens too quickly (a bit like opening a
pressurised can of fizzy drink) bubbles can form and cause DCS. A large part of diver training
is on what causes and how to avoid DCS.
Deco or Decompression:
The process of a diver 'returning to normal pressure' after a
dive and allowing the nitrogen absorbed (see above) to disperse. For more advanced diving
you have to stop on the way up and wait for your body to adjust to the new (reduced)
pressure, this is called a deco stop. Most diving is what is known as No Stop diving, just
coming up slowly is enough for the diver to decompress safely. Decompression continues when
the diver is back on the surface, after a days diving it can take over 24 hours for all the
extra nitrogen absorbed to fully disperse.
A special mixture of gasses (usually Nitrox or Oxygen) to be breathed during
a decompression stop. Breathing a high percentage of Oxygen, or pure Oxygen speeds up decompression.
Special training is needed in order to use Nitrox in general or to use it or Oxygen for decompression!
See our page on Pyle Stops
(or DSMB) See SMB
Demand Valve (DV):
The part of a regulator that you put in your mouth and breathe from.
It supplies air 'on demand' when you want it, the mechanics of a DV always supply you air at
absolute pressure, so a breath of air at 30m is actually 4 times the amount of air you would
breathe on the surface.
A CCR (see above) uses two gas supplies. Oxygen and diluent (normally compressed air).
When the Oxygen level is too low, Oxygen is added. The oxygen is metabolised into carbon dioxide and exhaled.
The CO2 is then cleaned (scrubbed) by an absorbant material and, if necessary, more oxygen is added.
A type of fitting for connecting the regulator 1st stage to the cylinder
pillar valve. There is a male screw thread on the 1st stage which screws into a female thread
on the pillar valve. The DIN fitting is the modern way of connecting the 1st stage to a
cylinder, it is used mainly on high pressure (300 BAR) cylinders, but used on most (if not all)
cylinders used in Technical diving for added safety.
Dive Timer (DT):
A simple electronic device for recording current depth, maximum depth
and time of a dive. Similar to a dive computer but it does not calculate decompression.
Different types of diving suits are used for different water temperatures
and diving conditions, the following is a brief summary - Lycra or Skin: A thin body stocking
used in tropical water, main purpose is to protect against abrasion and stings. Wet Suit: A
thicker neoprene material that works by trapping a layer of water between the body and the
suit, this forms and insulating layer. Semi-Dry Suit: An improvement on the wet suit, seals
at the wrist and neck limit the amount of water that flows in and out of the suit. Dry Suit:
Completely sealed from the water, dry inside. Diving dry suits have air valves that the diver
uses to inflate/deflate the suit, as well as insulation the suit can also be used for buoyancy control.
Most regular divers in cold waters use dry suits.
Dive Master. A PADI diver qualification, the first Professional rating.
Diver Propulsion Vehicle, or scooter. Used a lot in cave diving and some larger wreck
dives, but smaller DPVs are used in recreational diving to get to a reef or dive site out of swim distance.
A valve to allow the, or the action of, getting rid of (dumping) air from
a BCD or a dry suit.
DAN: Diver's Alert Network
Diving Equipment Manufacturers Association
Do(ing) It Right
Equivalent Air Depth. When using Nitrox as a breathing gas it has the effect of
'simulating' a shallower dive made breathing air, for dive time calculation purpoes
(see Tables) the EAD can be used for working out our no-stop time when using Nitrox.
EAN or EANX:
Enahnced Air Nitrox. Technically, it means a breathing mix made up of
Nitrogen and Oxygen, but with a higher than normal percentage of Oxygen (22-40% for recreational diving).
Some people interchange this with the term "Nitrox", although Nitrox means ANY mixture of Nitrogen and Oxygen.
Jargon for jargon's sake!
Emergency Cylinder. A small cylinder (0.4l) connected to the BCD. Can be used to
inflate the BCD and/or in conjunction with an Auto Air provide a very small redundant AAS. Not many people use them
anymore, as if they stick open you shoot to the surface!.
Equivalent Narcotic Depth. This is mainly used when diving with Trimix for calculations.
A Buddy that stuffs up a dive then insists its your round...
Fenzy (Frenzy) Bottle:
Another name for an EC.
Fuc*ed Up Beyond All Recognition.....(usually referring to a dive plan.)
Full Face Mask
Feet of Fresh Water
Feet of Salt Water
Breathing gas, usually air.
U-shaped attachment to the light head of an umbilical torch for attaching the light head to your hand.
Global Positioning System. Electronic navigation aid that uses satellites to give
a very precise read-out of your position. Originally designed for use by the US military.
Global Underwater Explorers. A technical training diving agency. See their website
Boundary between layers of water of different salinities
Hard Boat, a term used to describe a larger dive boat, typically an in-shore
trawler in the case of Irish diving.
A special breathing gas mix containing helium and oxygen only, this is usually a
comercial diving gas, TriMix is sometimes used for a very advanced form of diving.
HammerHead electronics made by Juergensen Marine for Rebreathers
High Intensity Discharge. A very energy efficient and expensive type of torch.
High Pressure. Normally used when taking about regulators, in the case of
regulator pressures high pressure is the current pressure in the cylinder, which could be
up to 300 BAR.
High Pressure Nervous Syndrome, only comes into play on very deep dives on Trimix.
It is a side effect of breathing Helium at high pressures.
A 5 yearly test to check the physical integrity of your tank
Too much Carbon Dioxide (CO2) in your bloodstream.
Too much Oxygen in your bloodstream.
Too little Oxygen in your bloodstream.
PADI's Instructor Development Course, made up of the AI and OWSI courses
PADI's dreadded Instructor Exam! Usually done immediately after the IDC or IOC
PADI's Instructor Orientation Course (for crossing over from another agency)
A popular rebreather model. See Ambient Pressure Diving
A technical, recreational, commercial and medical diver training agency.
See ITDA website
A technical diver training agency. See IANTD website
ISC: Innerspace Systems Corporation
(makers of the Megalodon rebreather)
A type of rebreather. It differs from most other CCRs in that while it senses
oxygen levels the diver is left to control them. See their website
A large and powerful underwater torch. Not usually as expensive as a HID.
Low Pressure. Normally used when taking about regulators, in the case of regulator
pressures low pressure is about 8 - 10 BAR.
London International Dive Show (usually in March)
See Diving Suits
A rigid tube that connects the two cylinders of a twin set together.
The manifold connects between the pillar valves of the cylinders, it sometimes has its own
'isolation' valve in the middle - in which case it is an isolation manifold.
Maximum Dive Time
A CCR rebreather, as used in the film The Cave. See their website: Megalodon
Metres of Fresh Water
Mixed Gas Rebreather
A term used to describe a breathing gas that is NOT normal air. Apart from
normal air Nitrox, TriMix, HeliAir and Heliox mixes are sometimes used.
Maximum Operating Depth
Metres of Salt Water
National Association for Cave Diving
National Association of Underwater Instructors
An 'altered state of mind' (effects can be similar to alcohol)
that effects divers at depth. Full name is Nitrogen Narcosis, it is caused by breathing
the nitrogen component of your cylinder under pressure. This is why deeper divers use TriMix - less Nitrogen.
No Decompression Limit
A breathing gas mix of oxygen (about 21% in normal air) and Nitrogen (about 79% in normal air).
Normally followed by a number that denotes the oxygen percentage - e.g. Nitrox 32 is a mix
containing 32% oxygen, 68% nitrogen. For recreational diving, the minimum used is 22%
and the maximum is 40%. Some people interchange this with the term "Enriched Air Nitrox",
although Nitrox means ANY mixture of Nitrogen and Oxygen.
National Oceanic and Atmospheric Administration
A type of dive where a decompression stop is not required.
National Speleological Society - Cave Diving Section
Open Circuit. Normal SCUBA gear, as opposed to rebreathers (Closed Circuit or Semi-Closed Circuit).
Open Water Diver (OW):
An entry-level diver qualification.
In diving terms this is a spare demand valve that is used as an AAS.
Any diving situation where there is no clear way up to the
surface, typically inside a wreck or a cave.
Open Water SCUBA Instructor. An entry-level instructor qualification.
Over Pressure (Relieve) Valve, or Over Pressurisation Valve
Oxygen Tolerance Test
Oxygen Toxicity Unit
Professional Association of Diving Instructors. An American based diver
training agency offering standard recreational and technical training throughout the world.
Certifying approximately one million divers per year, it is by far the largest diver
training agency in the world. See their website
Partial Pressure (PP):
One of the gas laws and a bit of mathematics that divers have
to put up with! It is to do with gasses in a mixture, put simply, it is the pressure of
one of the component gasses. e.g. A cylinder contains 25% oxygen, 75% nitrogen. A pressure
gauge shows that the cylinder is at 4 BAR, the partial pressure of the oxygen (ppO2) is
1 BAR, the pp of the nitrogen is 3 BAR.
Patent Foramen Ovale, openable flap between atria. See ASD.
A shunt between the right and left side of the heart that allows some blood to circulate
back through the body without going to the lungs first. This means that micro-bubbles don't
get removed from the blood stream by the lungs efficiently, making DCS more likely.
The metal fitting in the neck of a cylinder. Consists of an on/off
valve and a connection point for the regulator 1st stage.
A small (3ltr) cylinder with its own regulator that is carried as a redundant AAS.
(LP or HP) An off-take from the 1st Stage of a regulator.
See our page on Pyle Stops
An alternative (expensive!) type of scuba set. The normal scuba gear that
is used is known as 'open circuit', gases are not re-used. For normal scuba gear your body
only actually uses about 4-5% (it uses part of the oxygen content) of what you breathe, the
other 96% (plus the 4% carbon dioxide your body generates) you send to the surface as
bubbles. A rebreather works by 'keeping' what you breathe out, it cleans out the carbon
dioxide and tops up the 4% your body has used from a small cylinder. You then 'rebreathe'
this cleaned and topped up gas ad-infinitum (well, until your gas supplies run out).
Having a piece of equipment that is totally redundant under normal
circumstances, it is just there in case the main item of equipment fails. e.g. Many divers
carry two torches, a main torch and a smaller spare in their pocket. To be truly redundant
the equipment must not rely in any way on the piece of equipment that it is it is the back-up for.
Put simply, if you don't need it - don't bring it, if you do - bring two.
A drum, line and winder (like a large sea fishing reel) carried by a diver and
used for various things such as connecting to a SMB or as a 'back to where you started'
navigation aid. Origanally used in cave diving, then adopted by technical divers and recreational divers.
The collective term for the spider like collection of metal, tubes and bits of
plastic that divers connect to their cylinder and then to various other bits and pieces of
dive gear. It is made up of several parts, a 1st Stage, Demand Valve, Octopus, LP Inflators
Any dive undertaken when there is still nitrogen in your body from a
previous dive. See Decompression.
Rigid Inflatable Boat, rigid hull with large inflatable tubes down each side.
A purpose built dive boat owned by clubs and some individuals.
The collective name for a complete set of diving equipment (BCD, cylinder,
regulator...) used on a dive.
Remotely Operated Vehicle. These are used mainly in commercial and military operations. They have
electric motors with propellors and cameras that are linked by cable (umbilical) to the operator on
the surface. They can go far deeper that humans, and are a lot less expensive than a mini-sub.
You may have seen them in the film Titanic, amongst others...
Respiratory Minute Volume
Rule of Thirds:
Air - a third to get there, a third to get back, and last third is for emergencies.
Sub Aqua Association. A Diver Training agency.
Search And Rescue team
Semi Closed Rebreather. A rebreather that reuses most of the gas but lets some
escape, replacing it with fresh gas that contains a higher level of oxygen.
The part of the rebreather that removes carbon dioxide. Contains sofnolime.
Self Contained Underwater Breathing Apparatus.
A decompression stop, normally at about 5-6m, done just for safety.
Not actually required by the dive tables but most divers do a safety stop.
A recreational diver training agency. See SDI website
See Diving Suits
A rope with a heavy weight at one end and a buoy at the other. Dropped onto
a wreck or other sea bed feature and used to guide the diver to/from what they are diving on.
Complete loss of vision caused by silt being disturbed, typically by careless finning and/or bad bouyancy
Surface Marker Buoy. A surface float, normally filled with air, that the diver
controls via a line, it shows your cover boat (and anyone else) where a diver is.
Divers often carry a delayed SMB, it is carried rolled up in a pocket and it's deployment
is 'delayed' until the diver is preparing to come to the surface.
Steam Machines Incorporated (PRISM Rebreathers)
The chemical in a rebreather that removes carbon dioxide. Common
rebreathers contain enough to last three hours.
Trade name of a large 'aerosol' type device that is a complete cylinder
and DV in one small unit, carried as a redundant AAS, AKA Suicide Bottle (see below...)
A cylinder containing a breathing mix to be used during a decompression stop. AKA Deco Bottle.
Although the term "Stage Bottle" actually refers to leaving a bottle at a stage to come back to, not just a deco bottle.
A required (by the tables or the computer) decompression stop. Or a Safety Stop, which is not a decompression stop, but is done to offgas any excess nitrogen in the bloodstream.
An underwater photographers camera flash light. Also a small flashing light
carried on a BCD to let other divers know where you are.
Many think that emergency cylinders contain too little air to provide
much benefit, and that the risk of accidental inflation and subsequent injury from surfacing
too quickly is too high.
AKA Widow Maker - A type of brass clip with a springed gate notorious for trapping lines and killing divers
Society of Technical Risk-Optimizing Karst Explorers
Diver who's so clueless that he/she is a danger to him/herself and
anyone nearby. Often considered an accident looking for a place to happen. Diver who
refuses to learn even when shown a better way
Look-up tables that tell you how long and how deep you can safely go when you
dive. They tell you how long you can stay at a depth and still do a no stop dive, some tables
also tell you the decompression requirements if you stay longer than the no stop time.
A dive computer also does these calculations for you and keeps you constantly updated on your
decompression requirements during the dive.
Heart rate too fast.
A technical diver training agency. See TDI website
General term for an advanced form of diving involving special mixes
and decompression stops. Generically used for any type of diving beyond "normal" or recrational diving.
Boundary between layers of water of different temperatures
A specialised breathing mix consisting of oxygen, nitrogen and helium, used
for a very advanced form of diving, from 45m down. Trimix is used on all the Open Circuit Deep Dive record attempts.
Twin Set (or twins):
A diving rig comprising of two (equally sized) cylinders, both
of which are intended to be used during a dive. They are generally manifolded together.
Twin 12l tanks are normally used, but we have seen 7l, 10l, 15l and 18l tanks used also. 232 bar tanks are
the norm, but 300 bar are sometimes used, although the weight is significantly greater.
Another name for an Inspiration.
Visual test for your tank, essential every two and a half years
Short for visibility, the horizontal range of visibility when underwater.
Normally between 5m and 15m in Irish waters, sometimes more, sometimes less.
Vision Ears Nausea Twitching Irritation Dizziness (signs of the onset of Oxygen Toxicity)
See Diving Suits
Woodville Karst Plain Project (not to be confused with the Klu Klux Klan!)
Work of Breathing (how difficult it is to breath using your equipment.)
A type of BCD, most commonly used by technical divers.
Yellow Box Of Death. Yet another name for an Inspiration. Some point to several
deaths of divers using this particular rebreather, some of which haven't been explained, and say that
its unsafe. Others say that there are thousands of them being used successfully and that many
of the deaths were clearly caused by operator error. Everyone agrees that even the most
experienced OC divers are novices again when switching to rebreathers.
A special type of cylinder pillar valve. Instead of the normal one
connection point for a regulator 1st stage there are two, adding a second regulator gives