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Glossary - D

Daltons Law The total pressure of a gas mixture is equal to the sum of the pressures of each of the different gases making up the mixture.
DAN Divers Alert Network. A non-profit organisation that promotes the research and practice of safe diving.
DCI Decompression illness
DCMS Department for Culture, Media and Sport. DCMS administers the Protection of Wrecks Act 1973.
DCS Decompression sickness. A condition caused by Nitrogen bubbles forming in various parts of the body when a diver ascends too quickly and/or exceeds their ceiling. Also known as the bends The onset of DCS can be within minutes of the ascent, though usually within 1 to 3 hours and infrequently up to 12 hours.
DDRC  Diving Diseases Research Centre
Dead Reckoning Derived from the more correct term deduced reckoning, is an estimated position by measuring the distance run based on speed and direction of travel from the last known position. Used when there are no visible landmarks.
Decompression Chamber A chamber used for commercial divers, usually they are locked in at depth to be brought to surface under pressure for controlled and monitored decompression.
Decompression Line A line used as a point of reference or loose attachment for divers who are decompressing.
Decompression Sickness See DCS.
Decompression Stop The actual time to be spent at the decompression stop depth.
Decompression Stop Dive A dive which contains mandatory in water decompression or "offgassing" stops.
Decompression Theory The attempt to quantify gas dynamics in living tissues while exposed to hyper- or hypobaric environments.
Defogger A chemical defogging agent for face masks.
Dehydration The loss of bodily fluids, can contribute to DCS. In divers this can be brought about by diving with a hangover, consuming caffeinated beverages prior to diving, overexertion, or diving when ill. Immersion in water also produces a diuresis (production of urine by the kidneys) that can contribute to diver dehydration.
DEMA  Diving Equipment and Marketing Association
Demand Valve (DV) The part of a regulator that you put in your mouth and breathe from. It supplies air 'on demand' when you want it and at the right (absolute) pressure.
Depth Gauge A device that indicates to a diver how deep they are.
Derelict Property, whether vessel or cargo which has been abandoned and deserted at sea by those who were in charge of it without any hope of recovering it
Descent Rate The speed in which a diver descends. BSAC recommend 30m/min.
Deviation Effect of magnetic fields located near to a compass so as to cause errors in its readings.
Diluent An inert gas, usually nitrogen or helium, that provides volume in a breathing mix to ensure the partial pressure of oxygen remains within safe limits of exposure.
DIN (Deutsches Institut für Normung, or German Institute for Standardisation). Valve and regulator fittings featuring the "captured o-ring" design whereby the regulator is screwed into the cylinder valve. This is primarily used on the continent and for pressures exceeding 232 Bar.
Displacement The amount (weight) of water displaced by the boat or diver when floating.
Diurnal tides Diurnal tides occur in the pacific and have one high and one low water per day.
Dive profile The depth/time measurements of a particular dive usually expressed in a graphical form.
Dive Time The time from leaving the surface to the first decompression stop or 6m in no stop dives.
Diving Bell A weighted chamber, open at the bottom, in which a person can be lowered under water.
DM Dive Master. A PADI qualification.
DO Diving Officer.
Draft (Draught) The depth of water needed to float a vessel.
Drift Drift (speed) are the direction and rate of tidal stream and current.
DSMB Delayed Surface Marker Buoy. An inflatable, sausage shaped buoy that is inflated below the surface. It is attached to a reel held by a diver and is used to identify the location of underwater divers.
Drift Dive A dive where the diver just flows with the current.
Dump Valve A term for the exhaust fittings on dry suits, lift bags and BC's.
DVP Diver Propulsion Vehicle, an underwater scooter used to pull divers through the water.
Dyspnea Difficulty in breathing, in divers it can result from an increase in depth or density of breathing gas.










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Page last updated on October 16, 2007
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