Online Scuba Diving Terms A-Z 50/50
Nitrox50. 50% O2, 50% N2. Commonly used as a travel mix. 80/20 Nitrox80. 80% O2, 20% N2.
ABLJ
Adjustable buoyancy lifejacket. The horse collar style of buoyancy compensator. More commonly used in the past, nowadays rarely used.
Ab irons
Tool used to get abalone off rock.
Absolute
Pressure calculated by using a vacuum as the zero point and including the gauge and atmospheric pressure in the calculation.
Actual Bottom Time (ABT)
In repetitive diving, the total time actually spent under water (in minutes) from the beginning of descent until leaving the bottom for a direct continuous ascent to the surface or safety stop.
ACUC
American Canadian Underwater Certifications. Canada’s scuba certification Agency.
Adjustable Fin’s
Most commonly worn by scuba divers, generally larger and provide greater thrust
Adjusted No Decompression Limit
The time limit for a repetitive dive that accounts for residual nitrogen. Actual bottom Time should never exceed the adjusted no decompression limit.
AGA
A popular full face mask, the AGA Divator MKII.
AGE
Arterial gas embolism.
AI
Assistant Instructor
Air
A gas mixture containing 21% oxygen, 78% nitrogen, and 1% other gasses (mainly argon); compressed air is used for recreational scuba diving.
Air compressor
A machine that compresses or pressurizes air; for scuba purposes, air is compressed from the atmospheric level (14.7 psi at sea level) to the capacity of the tank, usually between 2500-3000 psi.
Air embolism
A condition that occurs when air enters the bloodstream through ruptured alveoli into the pulmonary capillaries. The air in the bloodstream then forms bubbles, which can block blood flow to the body’s tissues.
Air hog
Diver who sucks their tank dry in record time or at least much quicker than their dive buddy\
Air pressure
The force per unit area exerted by the weight of air; at sea level the air pressure is 14.7 psi.
Algorithm
A set of equations incorporated into diving computers in order to compute nitrogen uptake and elimination from changes in depth and elapsed time.
Alpha flag
International maritime signal flag, meaning, ‘Diver down, keep clear’.
Aluminum 80
Most common tank in industry. Nominal capacity 80 cu. ft.
Ambient Light
It is the available sunlight underwater used as a source of illumination.
Ambient pressure
The surrounding pressure; on land, comes from the weight of the atmosphere, at depth underwater calculated by the weight of the water plus the weight of the atmosphere. One atmosphere is about 14.7 pounds of pressure per square inch.
ANDI
American Nitrox Divers Incorporated
Anticoagulants
Medications that reduce the clotting ability of the blood. Particularly dangerous to divers due to barotraumas of air-filled body cavities.
AOW
PADI Advanced Open Water qualification
Argon
An inert gas that makes up less than one percent of air. Can be used as a gas for inflation in dry suits.
Arterial gas embolism
The condition characterized by bubble(s) of air from a ruptured lung segment under pressure; the bubbles enter the pulmonary circulation and travel to the arterial circulation, where they may cause a stroke. (AGE or CAGE).
Ascent Rate
The proper speed for ascending, which is no faster than 18 meters per minute. A rate slower is acceptable, and appropriate.
ATA
Atmosphere absolute; 1 ata is the atmospheric pressure at sea level; is measured with a barometer.
Atmospheric pressure
Pressure of the atmosphere at a given altitude or location.
AUF
Australian Underwater Federation
Backscatter
When suspended particles in the water are illuminated by light from a flash or strobe light reflecting light back to the lens. These particles appear as specks or snow like effect in the underwater photo.
Backward Roll Entry
Means of entering the water in SCUBA gear from a sitting position such as from the side of a boat whereby the diver, while securely holding his mask and gauges, leans backward and rolls into the water onto his tank and shoulders.
Back Gas
Tec Diving term for the gas in your doubles: usually the lowest oxygen mix to be used on your deepest part of your dive.
Bail-out bottle
Extra cylinder of gas carried by a surface supplied diver or a rebreather diver to enable them to reach safety in the event of an interruption of their primary supply.
Barodontalgia
Pain and discomfort caused by volume and pressure changes in teeth cavities.
BC or BCD
Buoyancy compensator or Buoyancy Compensation Device.
Bends
Common term for decompression sickness caused by dissolved nitrogen leaving the tissues too quickly on ascent causing bubbles formation. Believed that the term comes early divers suffering decompression sicknesses were bent over in pain from the effects.
Bladder
A plastic or rubber internal pouch within a Buoyancy Compensator which holds the amount of air injected into it or released from it to provide proper buoyancy for the diver.
Bleb
An abnormal pocket of air in the lungs, usually under the lining of a lung that can rupture with ascent and lead to barotraumas.
Blow a bag
Tec Dive slang for sending up a lift bag.
Blow up
Tec Diver slang for lose of buoyancy control causing an out of control ascent, especially with a dry suit.
Body suit
Garment made from various materials to provide full length abrasion and sun protection in the water.
Bootie
Divers foot ware, usually made of neoprene, worn inside an open-heeled fin; serves to protect the diver’s feet while walking to and from the dive site and prevents blisters from the fins while swimming; also provides warmth, depending on thickness. May come in a varying sole thickness.
Bounce or bounce dive
To dive and surface at intervals repeatedly. A dive where you turn around to ascend immediately after reaching the bottom.
Bow
The front end of a boat.
Boyle’s Law
States that if the temperature remains constant, the volume of a gas is inversely proportional to the absolute pressure; that if the pressure was increased, the volume must decrease proportionately and vice versa.
Breath-hold diving
Diving without means of Scuba or other life support apparatus. The Breath hold diver descends and ascends on one lung full of air.
Bubble
A collection of air or gas surrounded by a permeable membrane through which gases can enter or exit.
Bubble nuclei
Microscopic pockets of gas within the body into which inert gas may diffuse and form bubbles.
Buddy
Diving partner.
Buddy Breathing
Sharing of the same air supply by two or more divers. Can be used as an emergency technique when one person’s air supply is exhausted or unavailable due to equipment malfunction.
Buddy Check
Procedure carried out by SCUBA divers using the buddy system where each diver checks that the other's diving equipment is configured and functioning correctly just before the start of the dive
Buoyancy
The upward force exerted on an object in liquid. Objects that float are said to be positively buoyant, those that sink are negatively buoyant and an object that neither floats nor sinks but stays where placed is called neutrally buoyant.
Buoyancy compensator
An inflatable vest or jacket worn by the diver that can be automatically or orally inflated to help control buoyancy; 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.
Bust a stop
Tec diver slang meaning to skip a decompression stop due to error or emergency.
Bottom Time
The time from the beginning of your descent until the beginning of a direct and continuous ascent to the surface or safety stop.
Butt-mounting
Dangling the battery pack of a canister light underneath your doubles, rather than on the right hip.
BSAC
British Sub-Aqua Club. BSAC is the governing body for the sport of scuba diving in the UK. It is a club-based organization offering training for members through a large network of club branches, or through BSAC schools in the UK and around the world.
BWRAF
PADI training acronym: "Begin With Review And Friend". Alternatives: "Bad Women Really Are Fun"; "Big White Rabbits Are Furry"; "Boogie With the Rich And Famous"; “Big Women Really Are Fun”.
Canister light
A light where the battery is strapped to your belt and the light held in your hand.
Carbon dioxide
CO2; an odorless, tasteless gas that is a byproduct of metabolism; is excreted by the lungs in exhaled air.
Carbon dioxide toxicity
Problems resulting from buildup of CO2 in the blood; underwater with increased pressure and in accordance to Daltons Law high concentrations of carbon dioxide can more easily reach toxic levels with symptoms ranging from headache, shortness of breath, dizziness, confusion or even sudden blackout.
Carbon monoxide
CO; odorless, tasteless, highly poisonous gas given off by incomplete combustion of hydrocarbon fuels.
Carbon monoxide poisoning
CO bonds with hemoglobin and prevents blood cells from carrying oxygen. This causes oxygen deprivation in the tissues and can even cause death.
Carbon monoxide toxicity
Illness from inhaling excess CO; problems may range from headache to unconsciousness and death.
Cave Diving
Specialized Diving activity requiring specialized training and equipment to allow divers to safely dive 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.
Cavern Diving
Requiring specialized training, this involves diving into an overhead environment where unlike cave diving the exit should always be visible.
C-Card
Refers to a Divers certification card for a specific level of training undertaken.
CD
Course Director. PADI’s highest Instructor certification, authorized to conduct PADI Instructor training.
CDC
Career Development Center. PADI Training Facility Rating.
CESA
Controlled Emergency Swimming Ascent
Charles' Law
Charles’ Law says at a constant volume, the pressure of a gas varies directly with absolute temperature.
At a constant pressure the volume of a mass of gas is
proportional to the absolute temperature.
V1/T1=V2/T2
or
T x P = V
Chokes
A form of decompression sickness caused by enough bubbles entering the lungs to interfere with gas exchange; manifested by shortness of breath and can be fatal.
Closed foot fins
Have pockets that enclose the heal of the foot within the fin.
Cerata
Finger-like projections on the back of a nudibranch (sea slug).
Chart Datum (CD)
The level of the lowest tide there has ever been at a particular place. All depths on a chart and heights of tide refer to it.
CMAS
Confédération Mondiale des Activites Subaquatiques (World Underwater Federation of Underwater Activities). Established 1959.
CNS Hit
A convulsion caused by oxygen toxicity to the central nervous system.
Controlled Buoyant Lift
Underwater diver rescue technique used by scuba divers to safely raise an incapacitated diver to the surface from depth
Cummerbund
An overlapping waistband with Velcro used to secure a Buoyancy Compensator snugly around the diver’s waist.
Current
A horizontal movement of water; currents can be classified as tidal and non tidal; tidal currents are caused by forces of the sun and moon and are manifested in the general rise and fall occurring at regular intervals and accompanied by movement in bodies of water; non tidal currents include the permanent currents in the general circulatory systems of the sea as well as temporary currents arising from weather conditions.
Cutaneous DCS
Skin changes associated with decompression sickness; includes cutis marmorata, edema, and maculopapular rash.
D.A.N.
Divers Alert Network. Nonprofit organization that provides emergency and informational advice and assistance for diving injuries, promotes diving-related medical research and education, collects injury statistics, and offers dive safety services to its members and the diving community.
Dalton’s Law
Daltons Law states that the total pressure exerted by a mixture of gases is the sum of the pressures that would be exerted by each the gases if it alone occupied the total volume. This law is very important in explaining the toxic effects of gases at depth. eg Nitrogen Narcosis, carbon dioxide and carbon monoxide poisoning.
DCS
Decompression sickness
DCS/ DCI hit
To suffer from a decompression illness
Deco
Short for decompression
Decompression
Any change from one ambient pressure to a lower ambient pressure, always results in a reduction of gas pressure within the body.
Decompression Diving
Diving that requires planning stops during ascent to avoid decompression sickness. In recreational diving (no decompression diving), a decompression stop is considered an emergency procedure only, and is never an intentional part of the dive plan.
Decompression sickness
DCS; a general term for all problems resulting from nitrogen leaving the body when ambient pressure is lowered. Can be divided into Type I (musculoskeletal and/or skin manifestations only) or the more serous Type II (neuralgic, cardiac, and/or pulmonary manifestations).
Decompression stop
On ascent from a dive, a specified time spent at a specific depth, for the purpose of nitrogen off-gassing. Mandatory stops may be calculated in diving planning with tables prior to a dive or with the use of a dive computer.
Deep diving
For recreational sport divers a deep dive is a dive below 60 ft/ 18m.
DEMA
Dive Equipment & Marketing Association. Not-for-profit organization of equipment manufacturers, training agencies, dive media, travel companies and dive retailers that seeks to promote scuba diving and snorkeling to the general public.
Depth
The maximum depth in attained during a dive
Depth gauge
A device that indicates the depth below the surface that a diver is.
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.
Diaphragm
A dividing membrane or thin partition; the rubber (or other material) separating the demand chamber in a regulator from the surrounding water.
Diffusion
The movement of gases from areas of high concentration to areas of lower concentration.
DIN
Deutsches Institut fur Normung. Design of tank valve popular in Europe in which the first-stage regulator screws into the tank valve. Recommended for high pressure tanks. Regarded as superior alternative to a yoke fitting for first stage. Screws in rather than clamps on, and O-ring is "captured" inside valve, reducing chance of O-ring failure.
Disabled Diving
Special diving conditions and groups that offer the diving experience to people who have some kind of disability.
Diving
Scuba activity taking place beneath any body or water
Diver
Person qualified to participate in scuba activities.
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.
Dive Flag
May be either a red rectangle with a white diagonal stripe or a blue and white double tailed pennant. Flags are used to warn watercraft to stay away because there are divers below.
Dive lights
Specially designed underwater lights used for night, cave or wreck diving.
Dive Profile
A drawing of your dive plan, used to avoid confusion and omissions when using the dive tables.
Diving Regulator
Functions to reduce air pressure on demand from a scuba tank to ambient pressure
Dive Cylinder
Most commonly aluminum or steel high pressure tanks containing large volumes of dried compressed air.
Dive Booties
Molded sole neoprene boots for divers comfort, warmth, protection
Diving Mask
Restores the air space in front of the dives eye
Diving wet suit
Most common form of thermal and abrasion protection used by divers
Dive weight belt
Lead weight system to offset a diver’s positive buoyancy
Diver Integrated Wright’s
Weight’s integrated into the BCD
Dive Tables
A printed collection of dive times for specific depths, by which the divers can avoid contacting DCS. Most tables are based on Haldanian theory for nitrogen up-take and elimination.
Diver propulsion vehicle (DPV)
Motorized battery powered underwater vehicle or scooter used by divers to cover long distances underwater without having to kick.
DM
Dive Master
Double-disking
Using 2 burst disks on the valve of your tank to decrease the chance of losing all your air.
D rings
D-shaped rings. Attach to BC webbing with weight retainers.
Drift Diving
Type of recreational diving where the diver is transported by the currents caused by the tide or in a river.
Dry Suit
A water-tight garment that keeps the diver's body warm by providing insulation with a layer of gas, such as air, for diving in waters that are too cold for comfortable wetsuit protection, usually below 65'F.
DUI
Diving Unlimited International. Manufacturer best known for dry suits
Dump Valve
To vent air easily at the surface or underwater
Dysbaric Osteonecrosis
Permanent damage done to the bones and joints by long-term diving
Enriched air
(Sometimes called “Nitrox “) is air that has been “enriched” with oxygen so that it has more than 21% oxygen. For the purpose of recreational enriched air no decompression diving, you’ll be learning to use enriched sir with 22% to 40% oxygen.
Eanx 32
Enrich air blend with 32% oxygen and 68% nitrogen.
Eanx 36
Enrich air blended with 36% oxygen and 64% nitrogen.
EAD
Equivalent Air Depth. Enriched air dives are planned and calculated by using an equivalent air depth (EAD) and conventional air tables such as the RDP.
Ebb Current
A movement of tidal current away from shore or down a tidal stream; tide that is flowing out or causing a lower water level.
Eddy
A circular movement of water, in a comparatively limited area, formed on the side of a main current; may be created at a point where the mainstream passes a projection or meets an opposite current.
END
Equivalent Narcotic Depth. The depth at which air would cause as much narcosis as a given mix and depth. END is typically chosen to be 99 fsw or 132 fsw for a bottom mix.
Entonox
Mixture of nitrous oxide and oxygen (50-50). Dangerous to administer to divers.
Equalization
The act of gently forcing air into an open space to offset increasing water pressure.
Eustachian tube
A short tube connecting the back of the nose to the middle ear. If clogged, by mucus, equalization can be very difficult.
Exposure protection
Garments worn to prevent decreases in core body temperature and abrasions. Protection for divers can range from thin body suits to heavy dry suits.
Fast Tissue
A group of body tissue for theoretical representations that absorb and release nitrogen relatively quickly.
FFW
Feet of fresh water. Measurement of depth in fresh water.
Foramen Oval, Patent
Opening in the heart between the right and left atria that remains open in about 30 % of people, allowing passage of bubbles into the arterial circulation and symptoms of arterial gas embolism.
Forward Roll Entry
A method of entering the water while in full SCUBA gear from a boat transom or pier by bending at the knees, firmly securing the mask and gauges the rolling forward into the water landing on one's shoulders and tank.
Free Diving
Diving while holding your breath without any breathing apparatus.
FSW
Feet of sea water; used to indicate either an actual depth, or just a pressure equal to that depth (e.g., in a hyper baric chamber).
Gas absorption and elimination
Dissolved gases such as nitrogen are absorbed into the blood and tissues during the course of the dive. The level of saturation depends on the depth of the dive. The elimination of these gases is very important in preventing decompression sickness. The length of time required for elimination depends on the duration and depth of the dive.
Gas Laws
Laws that predict how gases will behave with changes in pressure, temperature and volume.
Gauge pressure
Pressure exclusive of atmospheric pressure, when diving, gauge pressure is due to the water pressure.
Granny line
Line which goes from the stern platform or hangbar to the anchor line.
Haldanian
Related to Haldane's theory that nitrogen is absorbed up and released in an exponential manner during a dive, and that there is some safe ratio of pressure change for ascent.
Half Time
Half the time it takes for a dissolved gas in a tissue (such as nitrogen) to equilibrate to a new pressure, or to reach full saturation at a new pressure. Theoretical tissue half times are used in designing dive tables and algorithms for dive computers.
Halocline
Boundary between layers of water of different salinities. Looks like a barrier of mist.
Hang
Tec Diving slang for hang time or time required to complete the decompression stop or stops.
Hang Bar
Bar slung underneath boat for convenience during safety and decompression stops
Hard Hat Diving
Surface supplied diving, generally in professional diving, either wearing a modern diving helmet or the old-style standard diving dress and brass helmet.
Head
Restroom on a boat.
Heliox
Mixture of helium and oxygen. Usually reserved for very deep diving.
Helium
Second lightest gas; does not cause problems of narcosis seen with nitrogen, and is therefore used for very deep diving.
Henry's Law
The amount of any given gas that will dissolve in a liquid at a given temperature is a function of the partial pressure of the gas in contact with the liquid and the solubility co-efficient of the gas in the liquid.
High Altitude Diving
Diving in mountain lakes or other high altitude waters at greater than 1,000 feet (300 meters) above sea level with increased risk of decompression sickness because of lower-than-sea-level atmospheric pressure at the surface; regular dive tables and some dive computers and depth gauges are inaccurate above sea level; special high altitude dive tables and recalibration of gauges and dive computers are required; specialty courses are available due to the complexity and added hazards of this activity.
High pressure nervous syndrome
Convulsions or seizure-like activity arising from high gas pressure at depth, especially with helium. Abbreviation is HPNS.
HWL
High water level
Hogarthian Principles
The Hogarthian configuration is named after Bill 'Hogarth' Main. It is based on reducing equipment to a minimum streamlined configuration that nevertheless includes sufficient redundancy for extended decompression dives.
Hoods
Diver garment worn over the head to reduce thermal loss.
Hookah
A surface-supplied compressed air apparatus, for use in shallow diving in calm waters. The air is delivered to one or more divers through a long hose.
Hydro
The common term for the hydrostatic test required on scuba cylinders every five years to determine whether the tank walls are still strong enough for safe usage.
Hydrogen
An inert gas, and lightest of all the elements, has been used in experimental diving situations.
Hydrostatic Test
Pressure test in which the dive cylinder is filled with water instead of air to the pressure of five thirds the maximum working pressure, causing the water to expand and be displaced.
Hyper baric Chamber
Air-tight chamber that can simulate the ambient pressure at altitude or depth. Hyper baric chambers are used in the treatment of decompression illness.
Hypercapnia
A higher than normal P02 level in the blood.
Hyperoxic and hyperoxia
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 partial pressure upper limit is generally considered to be approximately 1.6 ppO2 but in recompression chambers high levels may be used. When high partial pressures of Oxygen are inspired, convulsions may occur with little or no warning.
Hypercapnia
A higher than normal P02level in the blood.
Hyperthermia
A body temperature warmer than normal, less common in diving than Hypothermia, but can occur from overheating in a wet suit.
Hyperventilation
Over breathing to the extent that the blood carbon dioxide level is lowered, may lead to tingling in fingers and dizziness.
Hyperventilation
Over breathing to the extent that the blood carbon dioxide level is lowered, may lead to tingling in fingers and dizziness.
Hypothermia
A subnormal chilling of the body. A body temperature colder than normal (98.6F), severe problems start to manifest when body temperature reaches about 95'F
Hypoventilation
Under breathing to the extent that the blood carbon dioxide level is elevated, may be manifested by carbon dioxide narcosis.
Hypoxia
Lower than normal PO2 level in the blood, insufficient oxygen in the blood.
IANTD
International Association of Nitrox & Technical Divers
Immersion Hypothermia
Lowering of body temperature by full body immersion in cold water
In gassing
Taking on additional nitrogen and or other inert gases
Inner Ear
That portion of the ear in the petrous bone that has to do with hearing organs and balance
Isolating manifold
Manifold that also has a valve to isolate the two tanks, to preserve half the gas supply in the event of a failure.
Jetty
A structure, usually made with rocks, extended into a sea, lake or river to influence the current or tide in order to protect a harbor.
Jersey reel
A large spool designed to hold ¼ diameter sisal line. Used in conjunction with a lift bag.
Jon Line
Short line used to clip the diver to the anchor line while decompressing in a current.
Latent hypoxia
Sudden unconsciousness, from hypoxia, that occurs among some breath hold divers. Often occurs near the surface after a deeper dive. Same as "shallow water blackout."
Liebermeister's sign
Circumscribed pallor of the tongue associated with Arterial Gas Embolism.
Lift Bag
Air inflated bag attached by line to an object. When the bag is inflated the positive lift can be used to lift the object to the surface. Bags can come in many sizes depending on the required lift needed.
Lift Capacity
The amount of buoyancy provided by a Buoyancy Compensator or lift bag.
Live aboard
A dive boat with sleeping and eating accommodations. Commercial live aboard boats are usually between 50 and 130 feet long, and can carry from 10 to 30 divers for up to a week or more.
Long Hose
Tec diver name for the primary second stage on an approx 2.2m/ 7 foot hose that you can breath from or pass to another diver in an emergency.
Long shore current
A long shore current tends to push you down the beach-away from your intended exit area if you didn’t know to account for it.
LP hose
Low Pressure hose. Goes from 1st stage to 2nd stage or to inflator
LWL
Low water level
Kayak Diving
Alternative to boat diving or shore diving where the diver uses a special purpose kayak to get to the dive site.
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.
Marco Photography
A method of getting close-up pictures of a subject by using Marco accessories attached to the camera's lens.
MARES
Diving Equipment Manufacturer
Mask Squeeze
A painful condition when the air inside the mask is compressed by the external pressure creating suction on the face and eyes; can be alleviated by exhaling from the nose; can cause permanent eye damage if not equalized.
Mediastinal emphysema
Air from an over expanding lung escapes into the center of the chest. This puts pressure on the heart and major blood vessels, interfering with circulation. Symptoms are shortness of breath and feeling faint.
Middle ear
Air containing space of the ear bordered on one side by the tympanic membrane, which is exposed to any change in ambient pressure. Air pressure in the middle ear space can only be equalized through the Eustachian tube, which controls the middle ear to the back of the nose.
Mixed gas
Any non-air mixture that may include other gases such as helium within the mix.
MHW
Mean high water
MLW
Mean low water
MOD/ODL
Maximum operating depth/oxygen depth limit. The deepest that a diver can safely go using a particular gas mixture. For example, the MOD for EAN32 (32 per- cent oxygen) is 132 fsw (40 m).
Multilevel Diving
Spending time at several different depths on a single dive, starting with the deepest depth then progressively shallower. Planning dive profiles that credit you for slower nitrogen absorption when you ascend to a shallower depth. This provides more no-stop dive time. The Wheel version of the Recreational Dive Planner can be used for multilevel diving.
M value
The maximum calculated nitrogen tension allowed when ascending to a particular depth.
MSW
Meters of seawater: a unit of pressure. The pressure exerted by seawater varies slightly with temperature and salinity, but for practical purposes the convention is that each meter imposes a pressure of 0.1 bar. Sometimes the convention is that each meter is equivalent to 0.1 atmospheres (0.1013 bar).
NACD
National Association for Cave Diving
Night Diving
Dive at night, many underwater animals are nocturnal or behave differently at night.
Nitrogen
Inert gas that makes up 79% of air. Nitrogen is inert in that it does not enter into any chemical reaction in the body, but it can cause problems under pressure.
Nitrox
Any mixture of nitrogen and oxygen that contains less than the 79% nitrogen as found in ordinary air.
NOAA
National Oceanic and Atmospheric Association.
NASDS
National Association of Scuba Diving Schools. In 1999 NASDS merged with Scuba Schools International.
NAUI
National Association of Underwater Instructors.
Neritic zone
From the low-tide line to the edge of the continental shelf - around 200 m. After the neritic zone comes the pelagic zone - or open ocean.
Nitrogen Narcosis
Although nitrogen has no direct influence at the surface, that changes as you breathe it under pressure. Underwater, at depths approaching 30 meters/100 feet nitrogen has a noticeable intoxicating effect that intensifies as you go deeper.
No Decompression Limit (NDL)
The maximum time that can be spent at a depth before decompression stops are required. Also called “no-stop time.”
Normoxic gas
Air or other gas blend with 21% oxygen.
No-Stop Dive
A dive made within no decompression limits because you don’t have any required emergency decompression stops.
O2 (oh-two)
Oxygen or 100% oxygen
O2 clean
Clean enough of combustibles such as oil to allow use with high pressure O2.
Octopus Regulator (ocky)
An alternate second stage air source used by a diver's buddy in an out-of-air situation, or reserve 2nd stage regulator.
OEA
Oxygen enriched air - synonym for nitrox.
Off gassing
Reducing the load of nitrogen and or other inert gases
Omitted Decompression
Surfacing without having completed the decompression required by the computer or dive table being used.
Open circuit scuba
Apparatus used in recreational diving. Exhaled air is expelled into the water as bubbles; no part is re-breathed by the diver.
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.
Oxygen Therapy
Administration of any gas, for medical purposes, that contains more than 21% oxygen.
PADI
Professional Association of Diving Instructors
Partial Pressure
Pressure exerted by a single component of a gas within a gas mixture, or dissolved in a liquid.
Pneumothorax
An abnormal collection of air outside the lining of the lung, between the lung and the chest wall, often a consequence of pressure injuries (barotraumas).
Penetration Line and Reel
The penetration line provides a visual / tactile reference for finding your way out of the wreck, even if you are confused or unable to see due to silt.
Polluted Water Diving
Special equipment and procedures for diving in polluted waters. Skills used by Police, Military and Chemical inspection Diving Units.
Pony bottles
Are miniature scuba tanks with their own regulators, equip you with a completely independent air source
Prescription Dive masks
Dive masks with lenses produced especially for divers needing refractive correction.
Pressure
Any force exerted over an area.
PSI
Pounds per square inch, a common measurement of air pressure.
Purge Valve
Allow masks to be cleared without removal. Allows snorkels to be cleared easily.
Pressure Group
A letter used on the Recreational Dive Planner to designate the amount of theoretical residual nitrogen in your body.
Pulmonary Barotraumas
Rupture of the lung surface from increased pressure of ascent from depth. Usually due to closed glottis, pulmonary blebs or terminal airway disease. Causes arterial gas embolism, pneumothorax, and pneumomediastinum.
Pulmonary Edema of Diving
Fluid accumulation in the lungs secondary to immersion and pressure changes
Rebreather
A closed-circuit system which filters exhaled air then re-circulates it for rebreathing by the diver; requires special training and maintenance.
Recreational scuba diving
Diving to prescribed limits, including a depth no greater than 130 fsw, using only compressed air, and never requiring a decompression stop.
Regulator First Stage
Reduces cylinder pressure to ambient pressure plus a preset intermediate pressure
Regulator second stage
Reduces this ambient plus intermediate pressure to simple ambient pressure
Reference line
Descent and ascents are easier when you have a reference, and this is particularly true on a deep dive with limited visibility. A reference line is simply that a rope, usually ½ inch / 13 mm or larger, that you use for controlling ascents / descents, maintaining buddy contact and o simplify safety stops.
Relief Valve
To prevent BCD from rupturing due to over inflation
Repetitive Dive
Any dive done within a certain time frame after a previous dive; variable definition exists as to what time frame constitutes "repetitive." With some tables any dive within 12 hours of a previous dive is considered repetitive; when using a computer, any dive whose profile is affected by a previous dive is considered repetitive.
Repetitive Group
A letter used on dive tables to represent the amount of residual nitrogen in a diver.
Residual Nitrogen
The higher-than normal amount of nitrogen remaining in your body after a dive
Residual Nitrogen Time (RNT)
An amount of nitrogen, expressed in minutes for a specific depth, that you add to the actual bottom time of a dive to account for residual nitrogen from a previous dive.
Reverse Block
A reverse block occurs when expanding air cannot escape from an air space during ascent. In this case, you feel discomfort because the pressure inside the air space exceeds the surrounding water pressure.
Rip current
A rip current occurs when waves push water over a long obstruction such as a sand bar or reef. The water can’t flow out on the bottom, so it funnels back to sea through a narrow opening.
RIB
Rigid-hull inflatable boat
Rule of thirds
Overhead environments call for reserving two-thirds of your air for exiting the wreck; this includes the air you use from the time you leave the surface
SAA
Sub-Aqua Association
Safety Stop
A stop made between 3 and 6 meters usually 5 meters for three or more minutes at the end of a dive for additional safety. The safety stop is recommended after all dives (air supply and other considerations allowing), and required on those to 30 meters or greater, and those coming within three pressure groups of the no decompression limit.
Salinity
The amount of salt dissolved in a liquid, measured in parts per million.
Salt water aspiration syndrome
When the diver inhales a mist of sea water from a fault in the regulator second stage causing a reaction in the lungs.
SASY/SASA
Supplied Air Snorkeling for Youth/Supplied Air Snorkeling for Adults. BC-like PFD mounted with small compressed air cylinder and regulator that allows snorkeler to breathe comfortably on the surface but prohibits him from descending.
Saturation
The degree to which a gas is dissolved in the blood or tissues, full saturation occurs when the pressure of gas dissolved in the blood or tissues is the same as the surrounding pressure of that gas.
Saturation Diving
Diving performed after the body is fully saturated with nitrogen. To become fully saturated the diver must stay under water for a much longer period than is allowed in recreational scuba diving tables.
SCR
Surface consumption rate. Measure used in calculations for determining air consumption rate at various depths.
Scuba Resort
A resort facility providing recreation and entertainment to vacationers with the main attraction of scuba diving. It may include training, Beach and/or boat diving and many specialties such as wall, drift, wreck, eco-diving and many others. It can be an All-Inclusive, a Live Aboard and or a land base operation. It will normally be supported by one or many of the training agencies.
SCUBA
Self-Contained Underwater Breathing Apparatus
SDI
SCUBA Diving International. Qualification agency created in 1999. It grew out of sister company TDI, which specializes in the more advanced disciplines of technical dive training.
Semi dry suit
Wet suit with wrist and ankle seals to reduce the flow of water through the suit helping keep the diver warmer throughout the dive.
Shallow Water Blackout
A sudden unconsciousness, from hypoxia, that occurs among some breath hold dives. Often occurs near the surface after a deeper dive, hence "Shallow Water".
Shivering
The body's attempt to create heat through muscular activity.
Shore Diving
Scuba dive that starts from the shore
Silent Bubbles
Nitrogen bubbles, formed as a result of inadequate decompression but that do not result in any obvious manifestations of DCS.
Silt Out
Complete loss of vision caused by silt being disturbed
Single Dive
A dive whose decompression requirements are not effected by residual nitrogen from any previous dive or dives.
Skin Diving
Another name for breath-hold diving; diving without the use of a breathing equipment but may include a snorkel.
SLAM
Scuba Lifesaving and Accident Management. YMCA diver rescue course.
Slow tissue
A group of body tissue or theoretical representations of tissues that absorb and release nitrogen relatively slowly.
SMB
Surface Marker Buoy. Buoy with small dive flag and line to the diver
Software
Tec diver slang for specialized computer software used for creating custom dive tables.
Stage
To leave something to retrieve later, especially a stage bottle or decompression cylinder.
Squeeze
Pain or discomfort in an enclosed (sinuses, Middle ear, inside a mask), caused by shrinkage of that space, occurs on decent.
Stern
The back end of a boat.
Suicide Clip
Clip with a swinging gate, such as a marine clip. So called because they latch to things by themselves, sometimes causing entanglement hazards.
Surface Interval (SI)
The amount of time spent on the surface between two dives. It is usually recorded in hours: minutes (e.g. 3:25 - 3 hours, 25 minutes).
Super saturation
An unstable situation where the pressure of a gas dissolved in the blood or tissues is higher than the ambient pressure of that gas.
Surface supplied compressed air diving
Diving with the air continuously supplied by a compressor on the surface can be used for both sport and professional diving.
Swell
Caused by waves formed by past wind, or wind at a distance
Swimmer's Itch
Pruritic condition from diving in cercaria infested waters.
Scuba
Self containing underneath breathing apparatus
Snorkel
Allows divers to breathe at the surface without having to lift their heads from the water
SPG
Submersible pressure gauge
Tank Boot
Flat-bottomed, plastic, vinyl or rubber devices that fit over the rounded end of a scuba tank, allowing the tank to stand up.
TDI
Technical Diving International.
Technical Diving
Form of Scuba diving that exceeds the scope of recreational diving allowing for deeper and longer dives.
Tension
Partial pressure of a gas dissolved in the blood or tissue.
Thermo cline
Intersection between two layers of water of that are of distinctly different temperatures, usually the colder layer is deeper.
Tissue
A part of the body characterized by specific characteristics, such as muscle, bone, or cartilage. The term is also used to refer to any part of the body with a specific half time for loading and unloading nitrogen or even a theoretical compartment.
Tissue Compartment
Theoretical concept used to model groups of body tissues which are supposed to absorb and release nitrogen at a similar rate. Tissue compartments are used in the construction of most dive tables and dive computers. In most cases they are not meant to represent actual body tissues’
Travel Mix
Mix such as 50/50 used to travel to or from the bottom. Travel gas is used to get down to the point where depth indicates that you must change to your bottom mix, and then to get up from that point to where you can switch to your deco mix.
Trimix
Mixture of helium, nitrogen and oxygen, used for very deep diving.
Total Bottom Time (TBT)
The sum of Residual Nitrogen Time and Actual Bottom Time after a repetitive dive
Tumble
Clean tanks of internal corrosion, by filling them with an abrasive such as ceramic chips or aluminum oxide, and leaving on a machine that rotates them for several hours.
Turn Pressure
Pressure at which you end the dive or turn toward the exit, so that you end with the required reserve.
Tympanic membrane
The thin ear drums between the outer ear and the middle ear, visible to the examiner with an otoscope.
Upwelling
An upwelling is a slow-moving current commonly caused by offshore winds pushing the surface water away from shore. As the surface water moves out to sea, deep water flows up to take its place. The deeper water is usually clear and cold, crating excellent, though cooler, diving conditioning.
Vasoconstriction
The constriction of the blood vessels in order to reduce heat loss from the blood through the skin.
Vertigo
A sign of ear barotraumas and should not be ignored. Causes may range from minor ear squeeze to perforation of the eardrum to inner ear barotraumas.
VIP
Visual Inspection Program. Standardized visual tank inspection performed by a trained equipment technician, performed annually.
Visibility
The distance a diver can see underwater horizontally.
Wall Diving
Diving along the face of a vertical wall. Occurs on rock and reefs that run vertically, usually run from shallow to deep. Requires good buoyancy control because there is no seabed to prevent the diver descending too deep.
Water
1 part oxygen, 2 part hydrogen H2O
Weight Retainer
Small metal or plastic device used to keep lead weights from sliding or moving on the weight belt.
Weight System
Weights generally made of lead used to counteract the buoyancy of other diving equipment. These weights may be attached to a webbing belt or integrated into the BCD.
Wet Suit
Any suit that provides thermal protection underwater by trapping a layer of water betweens the diver's skin and the suit.
Wings
Tec diving BCD bladder, also a brand name of a BCD
Wheel
A dive table used to plan multilevel dives.
Windward
A point or side from which the wind blows; in the direction from which the wind blows; as opposed to, leeward.
Wreck Diving
Diving on natural or man-made shipwrecks.
Y-valve
Dual orifice tank valve
Zonation
The system used to describe fringing coral reefs. These reefs are commonly had six distinct areas (or zones): shore, back reef, flat reef, reef crest, fore reef and drop-off.
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