Diving Terminology
Actual Bottom Time (ABT): total elapsed time in minutes from leaving the surface until ascent is initiated
AGE: arterial gas embolism is a condition that can be caused by a diving accident in which a gas expands due to too rapid ascent, and a bubble and blocks the arterial flow of blood
Algorithm: a set of equations incorporated into diving computers in order to compute nitrogen uptake and elimination from changes in depth and elapsed time.
Altitude Diving: diving at a location where the water surface is 2000 feet above sea level or higher, and which requires specials dive tables or dive computers to calculate allowed depths and times for safety
Ambient Light: available sunlight underwater used as a source of illumination. "Natural light"
Ambient Pressure: the surrounding pressure; on land, comes from the weight of the atmosphere: at depth, comes from the weight of the water plus the weight of the atmosphere
Argon: an inert gas that makes up less than one percent of air
Atmospheric Pressure: the amount of pressure the air around us exerts on our bodies at sea level, about 14.7 pounds of pressure per square inch
Anoxia: absence of oxygen caused by inhaling a breathing gas that contains no oxygen or being unable to inhale any breathing gas
Aqua-lung: underwater breathing equipment consisting of a diving cylinder and diving regulator
Backscatter: when suspended particles in the water are illuminated by light from a flash, they reflect the light back at the lens. The particles appear as specks or snow in the photograph
Ballast: material used to improve the stability and control of a ship. In wooden ships usually stone, lead or iron; in metal ships, often water
Bends: a form of decompression sickness caused by dissolved nitrogen leaving the tissues too quickly on ascent; is manifested by pain, usually in the limbs and joints; "the bends" is sometimes used to signify any manifestation of decompression sickness
Barotrauma: is physical damage to body tissues caused by a difference in pressure between an air space inside or beside the body and the surrounding gas or liquid
Bounce dive: in recreational diving, a bounce dive is a descent to maximum depth and then an ascent back to the surface with the least delay, in a dive profile resembling a spike
Bow: front end of boat
Bridge: an elevated structure extending across or over the weather deck of a vessel, containing stations for control and visual communications
Buddy Breathing: two divers sharing a regulator or one diver providing a secondary regulator to another diver, generally after an out-of-gas emergency
Buddy System: pair or sometimes threesome of divers that dive together as a team for safety
Buoyancy Compensator: an inflatable vest worn by the diver that can be automatically or orally inflated to help control buoyancy; abbreviated B.C.
C-card or Certification card: proof of completed diver training and evidence of experience
D.A.N.: Divers Alert Network
DCS: see decompression sickness
Decompression: any change from one ambient pressure to a lower ambient pressure; always results in a reduction of gas pressures within the body
Decompression Sickness: a potentially lethal diving disorder caused by bubbles of inert gases, such as nitrogen or helium, coming out of solution and becoming trapped in the tissues, organs and blood vessels of the body causing symptoms ranging from rashes to death. Also commonly referred to as DCS, or DCI Decompression Illness
Decompression Stop: the depth at which a diver must stop on ascent for a specified period in order to eliminate inert gas before continued ascent
Decompression Tables: printed tables that provide divers with a way of avoiding Decompression Sickness by giving the maximum times that can be spent at depth, and by indicating the Decompression Stops and Surface Intervals needed for a particular depth and time profile to be carried out safely. Also know as Dive Tables
Depth Gauge: a device that indicates how far a diver is below the surface of the water
Dive Flag: flag used by a boat to indicate that it has 'divers down'. Comes in two versions: the international maritime signal flag (international code letter flag 'A',
Dive Profile: a two dimensional representation of the two most important characteristics of the dive that a diver must monitor to dive safely - depth and time. The profile is often used when describing a dive's likely decompression obligation.
Divemaster: a professional level diver who leads a group of less experienced divers underwater
Dive Tables: a printed collection of dive times for specific depths, by which the diver can avoid contracting DCS
Drift Diving: diving in a current
Drowning: death caused by inability to inhale anything but water
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
Dysbarism: medical conditions resulting from changes in ambient pressure
EAN: Enriched Air Nitrogen; Nitrox
First Stage Regulator: regulator attached to the scuba tank that lowers the tank pressure to ambient pressure + a pre-determined pressure (e.g., ambient + 140 psi)
Gas Blending: filling diving cylinders with gas mixes such as nitrox or trimix
Gas Embolism: a potentially lethal diving disorder caused by air or other gas bubbles entering the blood stream through wounds
Head: restroom
Heliox: a gas blend of Helium and Oxygen in which helium replaces the normal Nitrogen in air allowing diving at greater depths than can be done with air
Helium: second lightest gas; does not cause problems of narcosis seen with nitrogen, and is therefore used for very deep diving
HPNS: high Pressure Nervous Syndrome or Helium Tremors - caused by using breathing gases that contain helium at depth
Hydro: hydrostatic testing for tank integrity
Hyperbaric: having a pressure greater than that within the body tissues or fluids
Hypercapnia: carbon dioxide poisoning generally caused by rebreathing your own exhaled carbon dioxide - a problem at depth especially with rebreathers or high rates of exertion
Hyperventilation: either a deliberate and dangerous method intended to extend the duration of a free dive or the body's response to hypercapnia
Hypoxia: insufficient oxygen in the body - normally caused by inhaling a breathing gas that contains insufficient oxygen to support normal activities or consciousness
Hypothermia: a potentially lethal medical condition caused by cooling the body
Interstitial Emphysema: gas trapped in the chest after lung barotrauma
J-Valve: an early yoke style scuba tank valve that had a lever which activated a reserve pressure release and was commonly used before the submersible pressure gauge was available
K-Valve: a standard yoke style valve without a reserve lever
Log Book: list of the dives a diver has recorded for proof of experience
Maximum Operating Depth -MOD: the depth at which the partial pressure of oxygen (ppO2) of a gas mix exceeds a safe limit
Narcosis: depressed mental state, anywhere from confusion or drowsiness to coma
Nitrogen Narcosis: condition caused by breathing nitrogen at high pressure (at depth)
Nitrox: any mixture of nitrogen and oxygen that contains less than the 78% nitrogen as found in ordinary air
Oxygen Toxicity: is caused by using breathing gases that contain oxygen at high pressure (at depth)
Partial Pressure of a Gas: the concentration of individual component gases of breathing gases
Pneumothorax: collapsed lung
Port: left side of boat when facing bow
Rebreather: breathing equipment that captures, cleanses and re-oxygenates exhaled breath so that it can be re-inhaled
Recompression Chamber: a pressure vessel used to treat divers suffering from certain diving disorders such as decompression sickness
Regulator: in scuba, any device which changes air pressure from one level to a lower level (see first and second stage regulator)
Residual Nitrogen: nitrogen that remains dissolved in a diver's tissues after surfacing from a dive
Residual Nitrogen Time: the time it would take to off-gas any extra nitrogen remaining after a dive; in dive tables, RNT is designated by a letter A through Z. Residual nitrogen time is always taken into consideration in determining the safe duration for any repetitive dive
Saturation Diving: a decompression regime used in commercial diving that allows divers to live work for weeks at a time where their tissues become saturated in high pressure gas
Scuba: Self Contained Underwater Breathing Apparatus
Second Stage Regulator: the regulator that follows, in line, the first stage regulator, and delivers compressed air to the diver
Semi-Dry Suit: a wet suit with wrist and ankle seals to reduce entry and exit of water
Squeeze: pain or discomfort in an enclosed space (sinuses, middle ears, inside a face mask) caused by shrinkage of that space; occurs on descent
Starboard: right side of boat when facing the bow
Stern: the aftermost part of a ship
Subcutaneous Emphysema: gas under the skin tissue
Submersible Pressure Gauge or SPG: gauge attached to the regulator and used to monitor pressure remaining in the scuba cylinder
Surface Detection Aids: equipment, such as flags, SMBs, flares, EPIRBs and whistles, carried by divers to maintain contact with dive boats or attract rescue when lost at sea
Surface Interval: length of time on the surface, usually out of the water, between two consecutive dives
Surface Marker Buoy – SMB: a small inflated buoy that divers tow when underwater on drift dives to indicate their location to their boat
Technical Diving: a form of SCUBA diving that exceeds the scope of recreational diving allowing deeper and longer dives
Thermocline: intersection between two layers of water of that are of decidedly different temperatures; usually the colder layer is deeper – a diver can easily feel a Thermocline
Trimix: a breathing gas consisting of oxygen, helium and nitrogen
Visibility: the distance a diver can see underwater measured in feet or meters
Wall Diving: diving along the face of a vertical wall - requires good buoyancy control because there is no seabed to prevent the diver descending too deep
Wet Suit: a tightly fitting neoprene thermally-insulating diving suit that allows a limited volume of water inside the suit.
Windward: side facing into the wind; windy side
Wreck Diving: diving on shipwrecks
V-Valve: dual orifice (Y) Valve
