AAS
Alternate air source. A secondary regulator used by a diver in place of the primary regulator in order to make a safe, emergency ascent while still breathing normally.
Absolute pressure
The pressure that includes the effect of atmospheric pressure. When used with the unit 'atmosphere' it is abbreviated 'ATA'
A Clamp
A type of fitting for connecting the regulator 1st stage to the cylinder pillar valve. Also named Yoke.
Adsorbent
The substance that prevents carbon dioxide build-up in the breathing loop.
ADV
Automatic Diluent Valve. Automatic Diluent Injection in a Closed-Circuit Rebreather.
Air
A gas mixture containing 21% oxygen, 78% nitrogen, and 1% other gasses (mainly argon); compressed air is used for recreational scuba diving.
Air cell
A term used to describe a wing-style buoyancy compensator.
AGE
Arterial Gas Embolism. The result of a lung over-expansion. Also named CAGE.
Algorithm
A set of equations incorporated into dive computers in order to compute nitrogen uptake and elimination from changes in depth and elapsed time.
Ambient light
The surrounding light underwater that occurs naturally from the sun.
Ambient pressure
The surrounding pressure; on land, comes from the weight of the atmosphere. At depth underwater, comes from the weight of the water, plus the weight of the atmosphere. One atmosphere is approximately 14.7 pounds of pressure per square inch.
Analog device
A pressure gauge that uses a needle moving around a dial to provide tank pressure.
ANDI
American Nitrox Divers International, a technical dive training agency created by Ed Betts
Argon
An inert gas that makes up less than one percent of air. Very narcotic in the normal diving range, twice that of Nitrogen. It is a good insulator however and often used as drysuit inflation in cold water. Symbol is Ar.
Ascent/Descent line
A line suspended from a boat or a buoy that allows a diver to use as a means to control their rate of ascent or descent.
ATA
Abbreviation for atmosphere absolute; 1 ata is the atmospheric pressure at sea level.
Atlantis
The first version of the popular Dolphin, a semi-closed rebreather made by Draeger.
Atmospheric pressure
Pressure of the atmosphere at a given altitude or location.
Axial flow canister (or Axial scrubber)
An axial canister is a canister design in which the breathing gases move from top to bottom (or vise-versa) through the canister. Contrast this with "Radial canister".
Azimuth
A compass heading or angle. Also a model of Semi-Closed Rebreather.
Back gas
Breathing gas that is carried in primary cylinders on a diver's back.
Back plate
The center plate of a harness-style BCD. Can be constructed of aluminum, steel, ABS plastic or ballistic nylon.
Back up light
Dive lights carried as an emergency light in the event a primary light fails.
Bail out
A gas source the diver can switch to in an emergency in case of equipment failure. This can be either an external gas source with regulator, or it may be utilize a rebreather's diluent supply.
Bailout bottle
A tank carried on a dive that is designated for emergency use and not intended as a primary breathing gas.
Bailout Valve
See BOV.
Ballistic nylon
A tough, synthetic nylon fabric originally developed in WWII to protect wearers from flying debris and shrapnel. Ballistic nylon fabric resists tears and abrasions like no other fabric of its kind. Ounce for ounce, it is more durable than other fabrics: it's resistant to abrasions, tears, and scuffs and is a true high performance fabric.
Bar
Measurement of pressure slightly more than an atmosphere. 1 ATA = 1.0132 bar. 1 bar = 14.5083 psi.
BC or BCD
Abbreviation for buoyancy compensator.
Bezel
A rotating ring on a compass or watch.
Bladder
The inner air cell of a buoyancy compensator, which holds the amount of air used to provide proper buoyancy.
BOB
Bail Out reBreather. Twin-mounted and sling-mounted redundant rebreathers used to avoid carrying multiple Open Circuit bail-out tanks. (For more information, read the article about Bailout Rebreather Configuration).
BOV
Bailout Valve. Special mouthpiece for a rebreather that combines the usual DSv and an integrated second stage. (For more information, read the article about bailout valves).
Bottle
Slang term used to describe a scuba tank or cylinder.
Bottom mix
A gas that is specified for use at the deepest portions of a dive, usually when other decompression gases are present. Bottom mix may be air, nitrox or helium.
Bottom time
The time between descending below the surface to the beginning of ascent.
Bottom timer
A depth (pressure) activated time device that automatically starts as a diver descends. Can be mechanical or electronic.
Braided line
A woven nylon line that has better abrasion resistance than twisted line.
Breakthrough
Describes CO2 entering the inhalation side of the breathing loop on a Rebreather from the absorbent canister.
Breathing bag (Also called Counterlung)
A flexible bag in the loop that expands and contracts as the diver breathes, allowing for respiration and changes in the volume of the breathing loop.
Breathing loop
The breathing loop in a rebreather is composed of all the internal areas within which the breathing gases flow. This includes the counter-lung, canister, breathing hoses and the divers lungs.
Buoyancy
The upward force exerted on an object in liquid, whether the object sinks or floats. Objects that float are positively buoyant, those that sink are negatively buoyant and those that stay where placed are neutrally buoyant. cf Archimedes' Principle.
Buoyancy compensator
An inflatable vest worn by the diver that can be automatically or orally inflated to help control buoyancy; abbreviated BC or BCD (Buoyancy Control Device).
Burst disk
Thin copper disk held in place with a vented plug. Designed to rupture if tank pressure is greatly exceeded.
Bypass valve
A manual addition valve that allows direct addition of gas into the breathing loop on a Rebreather. Also called Manual Injector.
Cam band
The band that attaches a scuba cylinder to a BC by a 'camming' action when closing the buckle.
Canister (also called Scrubber)
The rebreather component that contains the CO2 adsorbent material. (For more information, read the article about ISC Radial Scrubber).
Canister light
A large, primary light with a battery pack contained in a canister. Typically has longer burn times than smaller, flashlight-style lights.
Caustic Cocktail
A highly alkaline (caustic) liquid producing a strong burning sensation, which can occur if water enters the rebreather canister and dissolves the adsorbent. It should be noted that condensation of warm moist gas on the colder canister is also a source of water which can cause a caustic cocktail. Also, the adsorbent reaction with CO2 also produces water vapor, which can then condense inside the canister.
Cave diving
Requiring much specialized training and equipment, this involves diving into an overhead environment including caves, abandoned mines or quarries and natural springs or sinkholes where the exit is not always visible. 'Overhead environment' means a structure exists which prevents the diver from making a direct vertical ascent to the surface. (For more information, read some cave diving expedition reports).
Cavern diving
Requiring specialized training, this involves diving into an overhead environment including caves, abandoned mines or quarries and natural springs or sinkholes; differs from Cave Diving in that the exit should always be visible. 'Overhead environment' means a structure exists which prevents the diver from making a direct vertical ascent to the surface.
CCR
Abbreviation for closed circuit Rebreather. (For more information, read the "Buyer's Guide to Rebreather Diving").
Celsius
Metric unit for temperature.
Channeling
Describes the settling of absorbent chemical in an improperly packed Rebreather scrubber. As the absorbent material settles, a passageway for exhaled, carbon dioxide-rich gas passes through the scrubber without having the carbon dioxide removed. Not a prominent problem in cartridge-style scrubbers.
Check valve
A valve that only allows a fluid or gas to flow in one direction. The mushroom valve used in a second stage regulator is one example. Check valves are also required in the hose assembly of a Rebreather, both on the inhalation and exhalation side of the loop to keep the gas flowing in the proper direction.
Cis Lunar
eCCR first manufactured in the USA (now in Sweden) and designed by cave explorer Bill Stone.
Closed circuit SCUBA
A SCUBA system designed to allow divers to re-breath exhaled air after removal of CO2 and addition of supplemental 02. In contrast to 'Open Circuit', closed circuit scuba is noiseless and produces no bubbles.
CO2
Carbon Dioxide. By-product of the metabolic process.
Computer
A device that monitors nitrogen in the body during a dive though mathematical algorithms. The device allows divers to multilevel dive and extend bottom time beyond what a dive table allows. (For more information, read a comparison between different dive computers).
Convulsions
One of the signs of Oxygen Toxicity. Extensively studied by Dr Kenneth Donald during WWII. (For more information, read the article about how to rescue an unconscious diver underwater).
CONVENTID
An acronym used to remember the central nervous system's signs and symptoms of oxygen toxicity:
CON: CONvulsions
V: Visual disturbances
E: Ear ringing
N: Nausea
T: Twitching, tingling
I: Irritability
D: Dizziness
CMF
Constant Mass Flow. A feature of some Semi-Closed Rebreathers.
CNS Toxicity
Central Nervous System Toxicity (see Oxygen Toxicity).
Counter-lung (Also called Breathing Bag)
A flexible bag in the loop that expands and contracts as the diver breathes, allowing for respiration and changes in the volume of the breathing loop.
cu ft
Abbreviation for Cubic feet, unit of volume (imperial system in the USA).
Cummerbund
The waist band on a buoyancy compensator.
Cylinder
The technically correct term for describing a SCUBA tank.
Dam
An anti-channeling dam is a small rubber ring installed inside a granular canister to ensure that gas is properly and efficiently channeled through the granular adsorbent. Failure to properly install a dam into a granular canister can lead to a diver experiencing hypercapnia.
DAN
Divers Alert Network. A not-for-profit organization dedicated to diver's safety, medical research and emergency.
DC55
French Military Semi-Closed rebreather used for mine clearance and manufactured by Aqualung.
DCI
Abbreviation for Decompression Illness (either AGE or Decompression Sickness). (For more information, read an article about Emergency Management in Remote Location).
Deco
Slang term for decompression.
Deco mix
A nitrox mix used to accelerate decompression. Can vary from a relatively low oxygen mix up to pure oxygen.
Decompression
Any change from one ambient pressure to a lower ambient pressure, always results in a reduction of gas pressure within the body.
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.
Decompression stop
A specified time and depth that a diver must remain to eliminate diluent/inert gas.
Deep diving
For recreational divers a deep dive is a dive below 18m/60 ft. For technical divers a deep dive is a dive below recreational limits of 40m/130 ft.
Deep stops
Pioneered by Richard Pyle, a scientific diver in Hawaii, who made careful note of physical symptoms after surfacing from numerous deep dives. Deep stops are found to help keep the diluent gas tension at reasonable levels during ascent.
Depth gauge
A device that indicates how far a diver is below the surface.
Descent/Ascent line
A line suspended from a boat, float or buoy used to permit divers to control their descents and ascents and to provide guidance to the bottom in poor visibility or strong currents; particularly useful on ascent to assist divers to make safety or emergency decompression stops between 3 to 4.5m / 10 and 15 feet.
Diaphragm first stage
A regulator first stage that uses a flexible diaphragm to keep water from contacting the internal parts, which helps to reduce corrosion or contamination.
Diluent
This is the gas used in a rebreather to make up volume in the breathing loop as the diver proceeds to deeper depths and the gases in the breathing loop are compressed. Depending on the rebreather, and the type of diving, the gas used for diluent could be air, nitrox, trimix or even heliox.
DIN
Deutsche Industrie Norm. Used to describe a valve connection for cylinder to regulator.
DIN valve
Identified by pressure rating of 200 bar or 300 bar.
DIR
Abbreviation for 'Doing It Right,' a term coined by a group of divers to describe a particular style of diving. The DIR system is much more than an equipment configuration. It is a diving style that ensures every aspect of each dive represents safety, fun and efficiency.
DIRrebreather
A team of Rebreather Divers applying safety concepts and standardization for CCR diving. For more information about DIRrebreather.
Dive computer
Device that constantly measures depth and time, based on a pre-programmed algorithm, the computer calculates tissue nitrogen uptake and elimination in several theoretical compartments and provides a continuous readout of the dive profile, including: depth, elapsed time of the dive, duration at current depth before decompression becomes mandatory, and a warning if the rate of ascent is too fast. (For more information, read a comparison between different dive computers).
Dolphin
A popular semi-closed rebreather made by Draeger.
Dosage device (or demand unit)
A regulator used in a semi-closed rebreather which delivers a constant amount of pre-mixed gas to the breathing loop.
Doubles
Two cylinders banded together and often connected by a manifold to allow longer dive time and redundant gas versus a single cylinder.
Down stream valve
A style of second stage design where the gas flow is always positive, flowing outward from the regulator so that in the event of a failure, it will fail leaking, not shut off.
DPV
Abbreviation for diver propulsion vehicle. Used to traverse quickly over long distances underwater. (For more information about Scooters and DPVs).
Drysuit
A water-tight garment that keeps the diver's body warm through the use of insulating undergarments.
DSV
Dive/Surface valve. Mouthpiece for a rebreather. It has two one way valves in it, one in each end. These allow breathing gas to flow in only one direction. The DSV will close off the mouthpiece from water with a lever located in the bottom of it.
EAD
Equivalent Air Depth. The depth relative to the partial pressure of nitrogen in a normal air mixture (21%O2, 79%N2). When there is a lower than normal fraction of nitrogen in a gas mix, the partial pressures of nitrogen are lower at any given depth. This allows the diver to feel less narcotic effect from the nitrogen than when breathing air at the same depth.
EAN
Abbreviation for Enriched Air Nitrox. May be used with numeric values to identify specific oxygen content of a gas such as EAN32.
EANx
Abbreviation for general nitrox values or where the specific oxygen value is not known or specified.
eCCR
Electronic CCR. The pO2 in the breathing loop is controlled by a computer.
Enriched Air Nitrox
A breathing gas that contains more oxygen than normal air and a corresponding decrease in the amount of nitrogen.
Evolution
A popular eCCR manufactured in the UK by Ambient Pressure Diving (Martin Parker).
Exhalation Hose
The exhalation hose is the breathing hose connected to the mouthpiece through which exhaled gases pass back from the diver to the rebreather.
Exhaust Bag
A flexible bag which accepts exhausted respirations from the exhalation hose. In this bag, excess pressure is vented through the exhaust valve out of the system. The remaining gas is passed onto the rebreather canister.
Exhaust Valve
This valve allows excessive gas to vent from the breathing loop. Expanding gas is vented upon ascent, or as gas accumulates in a semi-closed rebreather.
Exothermic
A chemical reaction which produces heat. When the canister chemically reacts with the CO2 in the loop, it converts it to calcium carbonate, water and heat, thereby warming the breathing gas.
Exposure protection
Garment worn to prevent decreases in core body temperature and abrasions. Protection can range from thin body suits to heavy dry suits.
Fahrenheit
The temperature scale used in the United States.
Fastex
These are the plastic quick disconnect fitting as per many BCs, etc.
Fathom
Unit used for measuring depths on marine chart (i.e. Forty Fathoms Grotto in Florida).
FFM
Abbreviation for a Full-Face Mask. (For more information, read the article about the Kirby Morgan M48 Full-Face Mask).
FFW
feet of fresh water. Measurement of depth in fresh water (imperial units in the USA).
First stage
Regulator attached to the SCUBA cylinder valve that lowers the tank pressure to ambient pressure plus a pre-determined pressure (e.g., ambient + 140 psi).
Flow meter
A visual indicating device that shows the flow rate, usually for an oxygen analyzer or to verify the flow rate in a Rebreather system. Is often used to describe a restricted orifice that 'meters' out gas for oxygen analysis.
Flow restrictor
A restriction placed in a flow line to keep the volume of gas limited. Commonly used with low pressure hoses to allow an oxygen sensor to accurately determine the fraction of gas without having to worry about variations in pressure caused by flow.
FSW
feet of sea water. Measurement of depth in sea water (imperial units in the USA).
Gaiters
Wraps that are used to squeeze the airspace in the lower legs of a dry suit to help maintain buoyancy control and body positioning (trim).
Galvanic corrosion
The corrosion that occurs when two or more different metals are placed in contact with each other. Depending on each metal's electro negativity, the rate of corrosion can be low or high. When water, particularly sea water, is added to the process, large amounts of metal can corrode away very fast.
Galvanized
A metal preservation and protection technique that uses thin rust resistant zinc coating on steel.
Gauge pressure
Pressure that does not include the effect of the atmosphere. Most SPGs as well as automotive tire gauges fall into this category.
GF
Gradient Factors. A mathematical way to tweak Buehlmann Decompression model in order to have deeper stops (Low GF) or longer shallow stops (high GF).
Gold line
Slang for the yellow nylon permanent line installed in cave systems in Florida and Mexico. Usually of kermantle construction for durability and long life.
GUE
Global Underwater Explorers. A Technical Diving Agency applying the DIR rules and created by Jarrod Jablonsky.
H valve
A dual outlet valve used with single cylinders to provide dual high pressure outlet for the use of dual regulators.
Haldanian
Referring to descriptions of gas mechanisms by J.S. Haldane, typically with tissue saturation and desaturation.
Hammerhead
An eCCR made in the USA by Golem Gear (Jakub Rehacek) and Juergensen Marine (Kevin Juergensen).
Harness
The webbing used to hold a backplate on a diver.
Heliair
A trimix made of heliuem and Air. Sometimes called "the poor man's Trimix".
Heliox
A breathing mixture of gases consisting entirely of helium and oxygen. This is used to eliminate nitrogen narcosis (by eliminating the nitrogen) and to control the affects of oxygen toxicity by reducing the oxygen in the breathing mix. Another benefit is reduced effort of breathing due to the lower density of helium.
Helitrox
A Trimix made of Helium and Nitrox.
Helium
Second lightest gas. Itdoes not cause problems of narcosis to the same extent as seen with nitrogen, and is therefore used for very deep diving. However helium distorts the voice and helium has less insulating value than an Oxygen/Nitrogen mix which results in divers becoming cold sooner. Symbol is He.
HID
Abbreviation for High Intensity Discharge. Technology used in underwater lighting that allows significant high power intensity lighting with very low battery power requirements. The color temperature is white-blue; more pleasing to the eyes.
HUD
Head-up Display. Mainly used for CCR, it gives the users some alarms about the breathing mix.
Hogarthian
The Hogarthian configuration is named after Florida cave diver, William 'Bill' Hogarth Main. It is based on reducing equipment to a minimum streamlined configuration in order to maximize gas efficiency, which including sufficient redundancy for extended decompression dives.
Hood
Garment worn over the head to reduce thermal loss.
HP hose
A hose specifically designed for high pressures so it will not rupture with dive cylinder pressures.
HPNS
High Pressure Nervous Syndrome is a condition which results from breathing helium under high pressures. Early symptoms of HPNS are sometimes seen as shallow as 90m/300 fsw but more commonly over 180m/600fsw. The early symptoms include muscle tremors, followed by changes in electroencephalogram (EEG) readings, impaired motor and problem solving skills. Other symptoms can include euphoria, nausea, vomiting, lack of appetite and drowsiness.
Hydrox
A mixture of Hydrogen and Oxygen. Experimental use in very deep commercial diving.
Hydreliox
A mixture of Hydrogen, Helium and Oxygen. Experimental use in very deep commercial diving.
Hypercapnia
Hypercapnia is the physiological condition that results from too much C02 (carbon dioxide). Typical symptoms are a shortness of breath and a headache. In extreme cases the final result is unconsciousness and eventual death from lack of oxygen. Skip breathing (using open circuit), hard work at depth, dead air spaces in the breathing loop and other problems can lead to hypercapnia.
Hyperoxic and Hyperoxia
In general, these terms relate to a more than a normal amount of oxygen. Hyperoxic refers to a mixture of gases with higher than normal oxygen content (above 21%). Hyperoxia is the physiological condition associated with breathing too high of a partial pressure of oxygen. The human body has a limit on both the partial pressure of oxygen it can tolerate and the long term dosage of oxygen. The partial pressure upper limit is generally considered to be approximately 1.6 ppO2 but most divers leave some margin for error and a more typical upper limit is 1.4 ppO2.
Hypoxic and Hypoxia
In general, both of these terms relate to a less than normal amount of Oxygen. Hypoxic refers to a mixture of gases with a lower than normal fraction of oxygen (less than 21%). Hypoxia is the physiological condition associated with breathing too low of a partial pressure of oxygen. When the ppO2 of oxygen falls below about .12, there is often not enough oxygen to maintain consciousness.
IANTD
International Association of Nitrox and Trimix Divers, a recreational-technical diving organization. Originally established by Dick Rutkowski, retired NOAA Deputy Diving Director, and Tom Mount.
IART
International Association of Rebreather Trainers, a german-based training agency.
Independent doubles
A technique of diving double cylinders without a manifold, requiring a complete regulator setup for each cylinder. Favored in some European countries and by sidemount divers.
Inflator valve
The valve on a buoyancy compensator where a low pressure hose from the second stage can be used for inflation. Usually includes an oral inflation mouthpiece.
Inhalation Hose
The inhalation hose is a corrugated, large diameter hose that allows a one-way flow of enriched gas from the inhalation or breathing bag through a checkvalve into the mouthpiece of the unit. The hose contains adjustable weights for diver comfort.
Inspiration
A popular and first commercially available eCCR made by Ambient Pressure Diving (Martin Parker) in the UK. (For more information, read the comparison between the Inspiration and the Megalodon CCRs).
Intermediate pressure
A step down pressure from the high pressure scuba cylinder to the ambient pressure at depth. Makes regulator function more stable and predictable. Common IP ranges from 8 to 12 bar / 120 to 180 psi.
IP
Abbreviation for intermediate pressure.
IWR
Abbreviation for In-Water Recompression. Techniques used in remote location when no recompression chamber is avaliable. (For more information, read the article about Emergency in Remote Location).
J-valve
An older style of cylinder valve with a spring activated reserve that served to release remaining cylinder gas for ascent. Used before SPGs were widely available.
Jon line
A length of line typically used to attach to an anchor line to provide spacing for decompressing divers at the same stop depth.
K valve
Standard on-off cylinder valve used on today's cylinders.
Karst
An irregular limestone geologic area that may have a series of sinkholes, fissures, cracks, caverns and underground streams caused by erosion by carbon dioxide enriched water.
Kelvin
Named after Lord Kelvin, a British physicist, it is the metric unit of thermodynamic temperature, where zero degrees Kelvin is defined as the point where atomic motion ceases (= -273.15 degrees Celcius).
Kg
Kilogram. Metric measure of weight.
Kit
British term for dive equipment.
Kiss
Abbreviation for "Keep It Simple Stupid", a philosophy that applies in many aspects of technical Diving. Also a model of Manual CCR made by Jetsam (Gordon Smith) in Canada (Classic Kiss and Sport Kiss).
LAR
A range of Oxygen rebreathers made by Dreager for military applications (LAR V, LAR VII).
LED
Abbreviation for light emitting diode. Light technology using diodes, rather than traditional bulbs, that are robust, rugged and have an incredibly long life compared to a conventional bulb.
Lift bag
A bag used by divers to float or lift objects underwater.
Lift capacity
The amount of buoyancy provided by a Buoyancy Compensator; varies according to size of the BC and according to the purpose of the BC, e.g., a BC intended for use in cold fresh water will provide greater lift capacity than one intended primarily for use in warm salt water.
Lorrain-Smith Effect
See Oxygen toxicity.
Low pressure inflator
An extra hose from the first stage regulator that provides air to inflate the BC.
Low volume mask
A mask which has a smaller area between the glass and the diver's face, usually with separate lenses for each eye; requires less air to purge if becomes flooded.
LPI
Low Pressure Inflator. Device used to inflate a BCD.
Manifold
Used on double cylinder systems. Has 2 valves similar to single tank systems attached by a heavy duty crosspiece with a valve in the center.
Mask
A skirted glass window constructed to provide air space between eyes and water and to permit both eyes to see in the same plane; a regular mask covers eyes and nose only; modern mask skirts are usually made of silicone rather than the older rubber ones.
mCCR
Manual CCR. Rebreathers where the oxygen injection is done manually by the user.
Megalodon
An american eCCR made by Innerspace System Corp. (ISC, Leon Scamahorn). The Meg comes in different flavours: Mini Meg, Standard Meg, COPIS Meg, etc). (For more information, read an article about the Megalodon CCR in deep diving).
Mixed gas
Any non-air mixture (e.g., trimix, nitrox), although some authors use the term only for mixes that contain a gas in addition to (or in place of) nitrogen (e.g., helium).
MOD
Abbreviation for maximum operating depth. The maximum operating depth of a breathing gas before reaching a predetermined maximum partial pressure of Oxygen, usually 1.6 or higher.
MSW
meters of sea water. Measurement of depth in sea water.
Multilevel diving
Spending a period of time at several different depth on a single dive.
Mushroom valve
The mushroom valve on a rebreather is the one way valve on either side of the mouthpiece which keeps the breathing gases traveling the loop in one direction. The valves are very important to ensure that the gases are scrubbed of CO2 and that there is enough O2 in the breathing loop.
NACD
National Association for Cave Diving.
NAUI
National Association of Underwater Instructors. It is one of the oldest diver certifying agencies.
NDL
No-Decompression Limit.
NEDU
US Navy Experimental Diving Unit.
NiMH
Abbreviation for Nickel Metal Hydride, a high capacity rechargeable battery. More tolerant to abuse and resistant to overcharging.
Nitrogen
Inert gas that makes up 79% of air. Nitrogen is inert in that it does not enter into any chemical reation in the body, but it can cause problems under pressure (see nitrogen narcosis, decompression sickness). Symbol is N2
Nitrogen narcosis
A narcotic effect produced by high partial pressures of nitrogen. This can affect judgment, and for most divers starts to be noticeable at a pN2 over 3.00 (approximately 30m/100fsw when breathing air).
Nitrox
Any mixture of oxygen and nitrogen which has more or less oxygen than air. The standard Nitrox mixtures are EAN32, EAN36 and EAN50 (EAN: enriched air nitrox).
NOAA
National Oceanic and Atmospheric Administration. Pioneer in Nitrox use for scientific diving.
No-mount
Method used to squeeze into small holes when cave or wreck diving. Requires diver to remove cylinders and push them ahead of the diver.
Normoxic
This is the term used to describe the normal mixture of gases found in the atmosphere. More specifically it refers to the percent of oxygen in the mix (a mixture of gas with 21% oxygen would be called normoxic).
NSS-CDS
National Speleological Society - Cave Diving Section
O-ring
Common sealing device for scuba equipment constructed of butyl, nitrile, Viton or EPDM. Measured by both its physical size as well as its hardness knows as 'durometer.'
Octopus regulator
An alternate second stage air source used by a diver's buddy in an out-of-air situation, or reserve 2nd stage regulator.
Open Circuit SCUBA
An underwater breathing device that supplies air to the diver (at ambient pressure, i.e. equal to the diver’s depth) from a tank with the resulting exhaled air being vented to the surrounding environment. The breathing circuit is "open", and the gas supply is not conserved by "rebreathing" it.
Open water diving
The recreational diving done in an environment other than a swimming pool but with no overhead obstacles; examples include lakes, ponds, rivers, oceans, quarries.
Optima (or O2ptima)
An electronic CCR made by Dive Rite in Florida.
OPV
Over-Pressure Valve. Release valve on a regulator, a dry suit or a rebreather loop.
OTS
Over-The-Shoulder counter-lung.
OTU
Oxygen Toxicity Units. Also called UPTD (Unit Pulmonary Toxic Dose) OTUs are a rough measurement of long term low ppO2 oxygen exposure. The units are only viewed as guidelines to help gauge whole body oxygen toxicity. They are based on the exposure to 1 ata of oxygen for 1 minute. 1ata for 1 minute = 1 OTU.
Ouroboros
An electronic CCR made in the UK by Closed-Circuit Research (Kevin Gurr).
Oxygen
Often seen as using the chemistry abbreviation 02, gas vital for all life on this planet; makes up about 21% of the air by volume.
Oxygen clean
Object that has been cleaned to remove contaminants that could react with high pressures of oxygen, specifically hydrocarbons (oils and silicones).
Oxygen compatible
Materials that are suitable for exposure to oxygen.
Oxygen sensor
Device to measure the PO2 in the loop, usually found in the inhalation bag of a rebreather. Also known as Oxygen Cell.
Oxygen Toxicity
Physiological damage resulting from higher than normal partial pressures of oxygen. There are two primary types of oxygen toxicity: one results from long exposures of elevated ppO2's (called "Lorraine-Smith Effect" or "Pulmonary Oxygen Toxicity" as the primary damage is to the lungs and airways), and the other results from short high ppO2 exposures (called "Paul Bert effect" or "CNS Toxicity" (Central Nervous System Toxicity)) and is characterized by convulsions with little or no warning signs. CNS toxicity usually occurs with ppO2 above 1.6.
Paul Bert Effect
See Oxygen Toxicity.
PFO
Patent Foramen Ovale. This is a foramen (a small oval opening) which is located the interatrial septum, the tissue between the atria, two of the four chambers of the heart. Everyone has this open hole in the heart prior to birth when it is needed in order for fetal circulation to bypass the lungs. A baby’s first breath should cause pressure in the left atrium to increase, so that the flap covering this opening closes and it normally eventually seals. Yet this valve flap stays loose in some individuals, causing an atrial septal defect or interatrial shunt called PFO.
P-valve
Drysuit accessory that allows a diver to void the bladder during a dive. Used in conjunction with a condom catheter.
pO2 or ppO2
The partial pressure of Oxygen in a gas mix.
pN2 or ppN2
The partial pressure of Nitrogen in a gas mix.
PADI
Professional Association of Diving Instructors. It is one of the largest SCUBA certifying agencies.
Partial pressure
The pressure of a particular gas within a gas mixture. In more specific terms it is the Fraction of the gas (F[x]) multiplied by the absolute atmospheres.
Polyurethane
Fifteen-mil polyether aromatic polyurethane is excellent at maintaining flexibility in low temperature environments and can be welded, which eliminates fittings and reduces failure points. It has very good chemical and abrasion resistance and excellent strength. It also resists the growth of microorganisms.
Pony bottle
A small scuba cylinder strapped to a divers main tank for emergency use.
PRISM Topaz
The PRISM (Peter Readey's Incredible Steam Machine) is an eCCR made by Steam Machines (Peter Readey) in the USA.
PSA (or PSAI)
Professional Scuba Association. One of the oldest Technical Diving Agency, created by Hal Watts.
PSI
Pounds per square inch, a measurement of gas pressure (imperial system in the USA). Also abbreviation for Professional Scuba Inspectors.
PSV
Passive Variable Ratio. Used with SCR-Calculations.
Radial flow
A radial flow canister is a canister design in which the breathing gases move from the middle to the outside (or vise-versa) through the canister. Contrast this with "Axial flow canister".
Ray
A Semi-Closed Rebreather made in Germany by Draeger.
RB80
A semi-closed rebreather made by Halcyon (Jarrod Jablonski) in the USA.
Rebreather
A self-contained device used to recirculate and regulate breathing gases for the purposes of extended diving times and quiet operation. On a fully-closed circuit rebreather this is accomplished by scrubbing CO2, and adding O2 as necessary to maintain a constant partial pressure of oxygen. On most semi-closed systems a portion of each breath is released to the water and the same portion of new breathing gases are injected into the system. The semi-closed system also uses a canister. (For more information, read the Buyer's Guide to rebreather Diving.
Recreational diving
Diving to prescribed limits, including a depth no greater than 40m / 130fsw, using only compressed air, and never requiring a decompression stop.
Redundancy
Technique of carrying back up equipment in the event of primary equipment failure during a dive.
Regulator
Device used to allow a diver to breathe gas from a high pressure cylinder at a suitable breathing pressure.
rEvo
A Closed-Circuit Rebreather made in Belgium.
RGBM
Reduced Gradient Bubble Model. It is a dual phase (dissolved and free gas) decompression algorithm developped by Bruce Wienke from the Los Alamos Laboratory, USA.
RMV
Respiratory Minute Volume. The amount of gas that a diver breathes out in one minute. The main controller of RMV is work rate.
Repex
A method developed by Bill Hamilton and used to compute the effect of oxygen during Repetitive Exposure.
SAC
Surface Air Consumption.
The volume of gas per minute at the surface.
Scooter
Slang term used for a diver propulsion vehicle.
SCR
Abbreviation for semi-closed Rebreather.
Scrubber
The part of a rebreather that removes excess CO2 from the breathing loop. This is accomplished through the chemical bonding of the CO2 with a reactive substance. In most current rebreathers the substance used is Soda Lime. There are a number of designs of scrubbers, but the two most widely used are axial and radial scrubbers.
SCUBA
Acronym meaning Self Contained Underwater Breathing Apparatus.
SDI
Scuba Diving International. The recreational scuba training and certification arm of TDI.
Second stage regulator
The regulator that follows, in line, the first stage regulator, and delivers compressed air to the diver. Usually associated with the mouthpiece.
Semi-closed circuit rebreather
A rebreather which vents part of the exhaled gases from the breathing loop as a function of each breath, RMV, or some other method.
Sentinel
A CCR made in the UK by Closed-Circuit Research (Kevin Gurr)
Service pressure
The pressure which a device is rated to work, not the test or hydrostatic pressure.
Setpoint
The desirable pO2 in a breathing loop of a rebreather. Either aumatically maintained by a computer and a solenoid valve in an eCCR, or manually controlled in an mCCR. For more information, read an article about Setpoint Selection.
Schraeder Valve
Standard automotive tire air valve. Also used in the Low Pressure Inflator with a Quick Connect.
Shutoff Valve
The shutoff valve on a rebreather mouthpiece is shut to prevent water from getting into the mouthpiece when the mouthpiece is not in the users mouth. Also known as Dive/Surface Valve.
Sidemount
Technique of carrying cylinders on the side of a diver to allow passage through tight restrictions or passageways. (For more information, read the article about sidemount configuration).
Skip breathing
The practice of inhaling, holding the inhalation for a period of time and then exhaling in order to attempt to extend the time underwater by using less air. This practice can lead to a buildup of CO2 and symptoms of hypercapnia. Skip breathing (which is not recommended) is used for open circuit diving only, and will have no effect on system duration of any rebreather.
SMB
Surface Marker Buoy. A small and highly visible lift bag sent to the surface by the diver.
Soda Lime
Sodalime (brand names: Molecular Products Sofnolime, W.R> Grace Sodasorb, Draeger Divesorb, Spherasorb, etc.) is a chemical agent which reacts and bonds with CO2 and is commonly used in granular canisters of rebreathers. The primary constituents of soda lime include Calcium Hydroxide - Ca(OH)2 (about 70-80%), Water - H2O (about 16 to 20%), Sodium Hydroxide - NaOH (about 1-2%), and Potassium Hydroxide - KOH (about >0-1%).
Solenoid
Electro-valve controlled by a computer, the solenoid is used to inject oxygen in the breathing loop of a rebreather.
Solo Diving
A controversial topic within the Technical Diving Community. (For more information, read the article about how to make Solo Rebreather Diving safer).
Sonic Orifice
Used as a dosage technique for some semi-closed rebreathers, the sonic orifice is designed to maintain the same gas flow, independent of the supply tank pressure. Sonic orifices are generally preset for a specific EAN mixture.
SPG
Abbreviation for submersible pressure gauge.
Stage bottle
A cylinder used to carry decompression gas to extend dive time or assist with decompression. Also called sling tank
Submersible pressure gauge
Gauge to monitor air supply during the course of a dive.
Suicide clip
Slang term used to describe boat clips that are notorious for snagging line as a diver traverses through a wreck or cave.
Table 6
The U.S. Navy treatment procedure for decompression sickness that is the most commonly used, consisting of oxygen breathing with air breaks at a maximum pressure of 2.8 ATA with typical treatment times of 285 minutes.
Tank
Slang term for scuba cylinder.
TDI
Technical Diving International. Technical Diving certification agency.
Technical diving
Term used to describe diving that is beyond typical recreational limits and/or diving in an overhead environment (wreck, cave, rebreather, trimix, DPV, etc). Technical divers are still recreational divers as opposed to commercial divers.
Thermocline
Thermoclines form when surface water heats from the sun with little or no water motion to mix it with deep water. Warmer water is lighter than cold water, so temperature layers develop with the warmer water lying on the surface.
Thirds Rule
A gas management policy of using one third of your gas supply for the initial dive penetration, one third for the exit, and hold back one third as a contingency reserve.
Tidal Volume
The quantity of gas that is inhaled and exhaled with each breath.
TLF
Total Loop Flooding. A serious condition that can happen to Rebreather Divers, making almost impossible to safely ascend while breathing from the loop.
Trim
An important component of a Technical Diver's comfort. (For more information, read the article about Comfort in Rebreather Diving).
Trimix
A breathing mixture of gases most often composed of oxygen, nitrogen and helium. This proportions of each are changed according to the needs of the particular dive plan to help limit oxygen toxicity and nitrogen narcosis.
Triox
A Trimix used for decompression.
Twinset
See Doubles.
Upstream valve
A valve that works against pressure, rather than flow with the pressure. When an upstream valve fails, it fails in the 'off' position, unlike downstream valves, which fail by free flowing.
UPTD
Unit Pulmonary Toxic Dose. See OTU.
V-weight
A weight placed between a set of cylinders to offset undesired buoyancy or trim.
VIP
Visual Inspection Program. Standardized visual tank inspection performed by a trained equipment technician, performed annually.
Viton
A trademarked perflourinated material used to make o-rings. More resistant to oxygen erosion that standard o-rings.
VO2max
Maximum Oxygen consumption at maximal workload.
Voting Logic
The way a rebreather computer assess the three oxygen sensors. If all three read close together, the two closest are averaged. If one is far off from the other two it is disregarded and an alarm sounds so you know a sensor has failed. Two of three oxygen sensors would have to fail at once to fool the computer—an unlikely event.
Voyager
A range of rebreathers made in Italy.
VPM
Varying Permeability Model. A decompression algorithm based on the behaviour of micro-bubbles dissolved in gelatin, and developed by David Yount. Later revised by Erik Baker and Ross Hemingway to become VPM-B and VPM-B/E.
Wetsuit
Any suit that provides thermal protection underwater by trapping a layer of water betweens the diver's skin and the suit.
Wing
A back mounted buoyancy compensator popularized by cave divers and later used by many technical divers.
WOB
Abbreviation for Work Of Breathing. The Work of breathing relates to the amount of effort required by the diaphram to move the breathing gases in and out of the lungs. Work of breathing is affected by many things on a rebreather including the hose diameters, valves, canister design, counter-lung placement and design, etc. The work of breathing is also affected by depth (depth increases the density which increases the work of breathing).
Wreck diving
Diving on natural or man-made shipwrecks.
What If's
An important phase of Technical Dive Planning: considering all potential problems that could happen and how to react.
Yellow Box of Death (or YBOD)
Historically this is what some Rebreather divers call the APD Inspiration CCR.
Y valve
A dual outlet valve used with single cylinders that is shaped in the form of the letter 'Y.' Also known as a sling-shot valve.
|
