Scuba Glossary: D - E - F - G
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 – The total pressure exerted by a mixture of gases is equal to the sum of the pressures of each gas of the different gases making up the mixture. Each gas acting as if it were alone were present and occupied the total volume.
Deco Mix – Gas mixture used during 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 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 illness – DCI; a term to encompass all bubble-related problems arising from decompression, including both decompression sickness and arterial gas embolism.
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 (neurologic, 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. When not mandatory it is called a safety stop.
Deep diving – For recreational divers a deep dive is a dive below 60 ft.
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 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 10 and 15 feet.
Diaphragm – A dividing membrane or thin partition; the thin muscle separating the chest cavity from the abdominal cavity; the rubber (or other material) separating the demand chamber in a regulator from the surrounding water.
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.
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 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 – Motorized vehicle used by divers to cove long distances underwater without having to kick.
DOT – Department of Transportation. U.S. government agency that regulates the manufacture, testing and transport of compressed gas containers, including scuba cylinders. DOT stamp appears on scuba tanks, followed by the alphabetic designation for the steel or aluminum alloy the tank is made of and the maximum fill pressure.
DPV – Diver propulsion vehicle, underwater scooter that allows a dive to cover an increased distance underwater. Popular at some resorts.
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.
EAD – The Equivalent Air Depth (EAD) is a way of approximating the decompression requirements of breathing gas mixtures that contain nitrogen and oxygen in different proportions to those in air, known as nitrox.
EAN – Enriched Air Nitrox. A N2/O2 (nitrogen/oxygen) breathing gas containing more oxygen (typically 32 or 36 percent) and less nitrogen than plain air. Used by recreational divers to increase either bottom time or safety margin by decreasing the amount of nitrogen absorbed. Requires pre-dive testing of gas mixture and adherence to strict depth restrictions.
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.
Equalization – The act of 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 is next to impossible.
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. F=(C/.556) +32
Fathom – A linear unit of measurement (equal to 6 feet) for water depth – commonly used by fishermen. Depth = V x T/2
ffw – feet of fresh water. Measurement of depth in fresh water.
First Stage – Regulator attached to the scuba tank that lowers the tank pressure to ambient pressure plus a pre-determined pressure (e.g., ambient + 140 psi).
Foramen Oval – The opening between the left and right atria of the fetal heart which remains open in about 30% of people, allowing passage of bubbles into the arterial circulation which is believed to cause symptoms of arterial gas embolism.
Forward Roll Entry – A method of entering the water while in full SCUBA gear from a boat transom or a pier by bending at the knees and, while firmly securing the mask, rolling forward into the water landing on one’s shoulders and tank.
Free Diving – Diving without any scuba or other equipment and synonymous with breath-hold diving.
fsw – feet of sea water. Measurement of depth in sea water.
FSW – Feet of sea water; used to indicate either an actual depth, or just a pressure equal to that depth (e.g., in an hyperbaric chamber).
Galley – Kitchen on a boat.
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 Analysis – A procedure whereby the fractions of gas in a breathing mixture are determined. Generally it is used to determine the fraction of oxygen to within 1 %, to control the effects of Oxygen toxicity. Most diving operations will analyze for oxygen only. In more complex Trimix’s, it is be desirable to analyze for the inert gases as well.
Gas Laws – Laws that predict how gases will behave with changes in pressure, temperature and volume.
Gas Saturation – Gas saturation occurs when the level of dissolved gas in a particular body tissue has reached its maximum.
Gauge pressure – Pressure exclusive of atmospheric pressure, when diving, gauge pressure is due to the water pressure.
GDAT – Gorman Dive Adventures and Travel
Giant Stride Entry – The most common method of entering water from a boat transom, pier, etc., where the standing diver takes a large step into the water while securely holding mask, tucking chin and bringing fins quickly together to keep himself at the surface for a controlled descent.
GoPro – GoPro cameras. Hero 3 Black, Siver and White. Miniature camera for all sports, above water and under. GoPro is a brand of the privately owned San Mateo, California company Woodman Labs that features “wearable” camera/camcorders such as helmet cameras that are targeted at adventure video/photography.
GPS – Global positioning system. A worldwide system of navigation based on a ring of stationary satellites. Small, even handheld, GPS devices can be used to accurately determine speed and direction of travel, and pinpoint dive site locations.
Granny Line – Also known as a Gerry Line. A line which goes from the stern platform or hang bar to the anchor
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