Glossary

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

A	AAS	Alternate Air Source, second demand valve or regulator, sometimes referred to an octopus.
	Absolute Pressure	Absolute pressure is a measure of the pressure exerted on an object from all sources; includes water pressure and atmospheric pressure.
	ABLJ	Adjustable Buoyancy Life Jacket. An older style of buoyancy device still used by some divers.
	A Clamp	A type of fitting for connecting the regulator 1st stage to the cylinder pillar valve.
	ACI	Assistant Club Instructor. A BSAC instructor qualification.
	ACR	Air Consumption Rate, same as SAC, Surface Air Consumption.
	AD	Advanced Diver. A BSAC diver qualification.
	AGE	Abbreviation for Arterial Gas Embolism. See CAGE.
	AI	Advanced Instructor. A BSAC instructor qualification
	Air embolism	Bubble of air in the blood stream.
	Alveoli	Small air cells in the lungs.
	Ambient pressure	The surrounding pressure; on land this comes from the weight of the atmosphere; at depth it is the sum of both the weight of the atmosphere and the weight of the water.
	Anoxia	The total lack of Oxygen to the tissues. Also see Hypoxia
	AOW	Advanced Open Water. A PADI diver qualification
	Apnea	Cessation of breathing for short intervals of time. If left untreated it will proceed to respiratory arrest.
	Argon	An inert gas which is very narcotic in the normal diving range, twice that of Nitrogen. It is a good insulator however and sometimes used in diving suits.
	Ascent Check Depth	A point reached during the ascent where dive time is checked against the plan. This is usually at the first decompression stop or 6m for no-stop dives.
	Ascent Rate	The speed in which a diver ascends. BSAC recommend 15m/min up to 6m and then 6m/min for the final 6m.
	Atmospheric Pressure	The local atmospheric pressure produced at a particular altitude by current weather conditions.
	Auto Air/Air II	A form of alternate air source build into BuddyT stab jackets.
	AV	Artificial Ventilation
B	Backup	The concept of carrying fully functional backup systems to replace primaries in the event of failure.
	Bailout	A small cylinder, (usually 3-4 litre) commonly used as an emergency breathing system in commercial diving, also known as a Pony bottle.
	Bar	A measure of pressure, 1 bar = atmospheric pressure or about 15lbs per square inch.
	Barodontalgia	Pain & discomfort caused by the volume and pressure changes in teeth
	Barotrauma	Injuries resulting from the inability of expanding gasses to exit the body. For example, ear drum rupture, lung over expansion injury, pneumothorax, squeeze, sinusitis.
	BCD	Buoyancy Control Device, sometimes called a stab jacket (stability). An inflatable jacket worn by divers. This provides buoyancy and holds the diving cylinder.
	Bends	See: DCS
	Bottom Mix	A breathing mixture used at the deepest portion of a dive.
	Bottom Time	Often calculated from the start of the diver's descent until the beginning of his ascent, or to the safety stop or first decompression stop. Note: This measurement varies widely from organisation to organisation, and some divers do not calculate the safety stop into their total bottom time.
	Bradycardia	A heartbeat of less than 60 beats per minute.
	BSAC	British Sub Aqua Club.
	Buddy	Your diving partner. BSAC strongly recommend that divers always dive in pairs for safety.
	Buddy Breathing	An emergency out-of-air procedure where two divers share one second stage regulator while ascending to the surface.
	Buddy Check	A pre-dive check where two divers familiarise themselves and check each others equipment prior to a dive.
	Buoyancy	The upward force equal to the weight of water which is being displaced by an immersed object.
C	CAGE	Coronary Arterial Gas Embolism. A lung over-expansion injury that involves air bubbles escaping from the lungs into the pulmonary capillaries. The bubbles can then travel to the heart and eventually follow the circulatory route to the brain. In severe cases, CAGE can be fatal. Treatment is immediate O2 breathing and transport to a recompression chamber. Also known as air embolism. Symptoms may be similar to DCS.
	Carbon Dioxide (CO2)	A gas generated by the metabolic process of generating energy to sustain life. Carbon Dioxide "CO2" is normally regulated through the breathing process where CO2 (with its high dissolved PPCO2) is moved out of the bloodstream, and Oxygen (with its high ambient PPO2) is moved into the bloodstream. In normoxic air the percentage of CO2 is negligible, about 0.03%. CO2 appears to be a factor in DCS, narcosis, hyperoxia and Hypoxia.
	Carbon Monoxide	Carbon monoxide (CO) is produced from the incomplete combustion of organic fuels, most commonly gasoline engines. Carbon monoxide is a colourless, odourless, tasteless gas, and it is largely because CO cannot be readily detected that it is so dangerous. Inhaled CO will bond with haemoglobin with an affinity 200 times greater than oxygen.
	Cardiopulmonary Resuscitation	A process utilising the combination of external heart massage and mouth-to-mouth respiration (artificial ventilation) to artificially maintain the heartbeat and respiration of a victim.
	Celsius	A unit of measure for temperature. Celsius = (Fahrenheit - 32) / 1.8 or 5/9 (Fahrenheit -32)
	CI	Club Instructor. A BSAC instructor qualification
	Computer	An electronic device either worn on the wrist or console mounted which constantly displays information such as current depth, maximum depth, dive time and remaining no stop time. It can also calculate the decompression requirements for the dive and provide other information such as temperature ascent rates etc...
	CNS	Central nervous system
	CNS Oxygen Toxicity	The effects of breathing high-pressure O2. An extremely dangerous manifestation which can include convulsion and collapse. Although 1.6 Bar has been held as the standard limit by NOAA, many divers prefer to restrict their activities to no more than 1.4 Bar PPO2 for added safety. Recent tests by the US Navy suggest that CNS O2 Toxicity can be seen as low as 1.3 Bar PPO2. CNS O2 toxicity can be prevented by a reduction in the PPO2 in the breathing gas via a different gas mixture or via ascending.
	CPR	Cardio Pulmonary Resuscitation
	Current Tissue Code	The code which identifies a divers current nitrogen saturation level. Calculated from the last dive's surfacing code and the surface interval.
	Cyanosis	A bluish discoloration of the skin that results from an oxygen deficiency in the blood.
	Cylinder Markings
D	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.
	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.
	Decompression Line	A line used as a point of reference or loose attachment for divers who are decompressing.
	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.
	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.
	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.
	Descent Rate	The speed in which a diver descends. BSAC recommend 30m/min.
	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.
	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.
	Dump Valve	A term for the exhaust fittings on dry suits, lift bags and BC's.
	Dyspnea	Difficulty in breathing, in divers it can result from an increase in depth or density of breathing gas.
E	EAD	Equivalent Air Depth. A means of equating gas mixes (such as Nitrox) to air.
	EANx	Enriched Air NITROX. A mixture containing more than 21% oxygen.
	END	Equivalent Narcosis Depth. Means of equating the relative narcotic influence of inert gases to air. See EAD
F	Fahrenheit	A unit of measure for temperature. Fahrenheit (1.8 * C) + 32 or 9/5C +32)
	First Stage	The part of the regulator that connects to the cylinder. It acts as pressure reducing valve that reduces the cylinder pressure (typically 232 Bar) to about 10 Bar. This is connected to a hose to the demand valve or second stage.
	FSW	Depth measured in feet of sea water.
	Full Face Mask	A diving system with the regulator built into a diving mask that completely covers the face, nose and mouth. Provides extra safety margin with high PO2 exposures (helps prevent drowning in case of a seizure) and is easily adaptable to communication units.
G	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 analyse for oxygen only. In more complex Trimix's, it is be desirable to analyse for the inert gases as well.
	Gas Consumption	(RMV)*(Bar) = gas consumption at depth. Total gas required for a dive= the sum of the gas required at each stage of the dive. Gas required at each stage of the dive=(Bar) x (RMV) x (Time) x (Work modifier). Bar= Pressure at each stage Bar=(depth / 10)+1 RMV= Respiratory Minute Volume (in litres per minute) Time= Time in minutes spent at that stage/depth Work=A modifier to take into account that you breath more when working. 1, at rest 1.5 working mildly 2 working moderately 3-5 working heavily Descent consumption = average depth plus time spent descending. Gas consumption during ascent is calculated by "average depth" method: (max. depth + 1st deco stop depth)/2. This average depth is then used in the gas consumption equation.
	Gas Mixing	Gas mixing or blending is accomplished via one of four different ways: 1. By partial pressure, where only the pressures of the constituent gases are considered in determining their percentages in the final mix. 2. By continuous flow, where the appropriate amount of each gas is metered and injected into a gas flow stream, and then delivered to a mixing chamber or compressor inlet. 3. By volume, where known volumes of each gas are delivered to a container near atmospheric pressure, then compressed into high pressure cylinders. 4. By weight, where the gases are proportioned in the final mixture by the weight that each gas adds to the initial weight of the container.
	GPS	Global Positioning System. An electronic navigation device that uses satellites to give a precise display of your position.
H	Heliox	A breathing gas consisting of a mixture of Helium and Oxygen.
	Helium	A gas which is easily eliminated from body in long dives and builds up fast in short dives. It is the least narcotic of standard gases and causes that "micky mouse" voice effect. It is a poor insulator and moderately costly.
	Haemoglobin	The most important constituent of the red blood cell is the molecule of haemoglobin, an iron containing protein that has the ability to unite with oxygen and transport it to cells throughout the body it also combines with CO2 and adds in the transport and removal of CO2 from the body.
	Hydrogen	A gas that is easily eliminated from the body in long dives and builds up fast in short dives. It has a slight narcosis affect at depth and cause a large voice distortion:
	Hydrostatic Pressure	The pressure exerted underwater by the surrounding water column.
	Hydrostatic Test	A test that is required every five years on SCUBA cylinders. This test involves pressurising the cylinder to test pressure.
	Hydrox	Breathing gas consisting of a mixture of Hydrogen and Oxygen.
	Hyperbaric	Dealing with pressures greater than 1 bar.
	Hyperbaric Chamber	A recompression chamber.
	Hypercapnea	An undue amount of CO2 in the blood caused by improper breathing habits and incomplete scrubbing of breathing gases in closed circuit re-breathers or excessive amounts in the breathing mixture. As concentrations of CO2 approach a PPCO2 of 0.10ATM symptoms begin to appear. Confusion & drowsiness, then muscle spasms, rigidity and unconsciousness. High PPO2, high gas density and high breathing resistance add to the severity of Hypercapnea. Treatment is a reduction of the PPCO2 and administration of oxygen.
	Hyperoxia	Elevated oxygen levels in the tissues. See oxygen toxicity, CNS oxygen toxicity.
	Hyperthermia	Inadequate loss of heat from the body resulting in a rise in core temperature. This is most commonly seen in areas with high ambient temperatures and divers with low body fluid levels.
	Hyperventilation	The process of rapidly inhaling and exhaling to purge the body of carbon dioxide, thus decreasing the natural urge to breath. Hyperventilation is a potentially dangerous practice and can lead to, hypocapnia, shallow water blackout, unconsciousness and drowning.
	Hypobaric	Dealing with pressures less than 1 Bar
	hypocapnia	An insufficient amount of CO2 in the blood (defined as pCO2 levels less than 35 mmHg), often the result of hyperventilation.Hypocapnia can cause weakness, faintness, headache, blurred vision and if untreated possibly unconsciousness. The body's breathing stimulus results from the monitoring of the CO2 and oxygen (the oxygen drive is only active at extremely low oxygen levels, CO2 is the MAJOR controlling factor) levels in the blood stream. An increase in CO2 and a decrease in oxygen trigger the body to breathe. As the CO2 levels drop, so does the body's natural stimulus to breathe. This is one of the primary causes of shallow water blackout.
	Hypothermia	A condition in which the deep tissue or core temperature of the body falls below the normal physiological range, approximately 36.9C. Heat loss is the result of exposure to cold, and most divers are exposed to water temperatures below that of their body. The rate of the heat loss is dependent on body area, the difference in the temperature between the body and the surrounding environment, body fat, external insulation and the level of physical exertion. As the core temperature begins to drop signs of hypothermia will begin to appear. This will trigger the body to begin producing extra heat, usually in the form of shivering. If the cooling is allowed to continue the core temperature will begin to drop and all bodily processes will slowly grind to a halt as pulse and respiration's slow. Death will follow if the diver is not treated promptly.
	Hypoxia	A Condition brought on due to an insufficient Partial Pressure of Oxygen (PPO2) in a breathing gas. A failure of the tissues to receive sufficient Oxygen.
I	IANTD	International Association of Nitrox and Technical Divers
	Inert Gases	Those gases present in a breathing mixture which are not metabolised.
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L	Lifting Bag	A bag like device that is inflated underwater to lift objects from the bottom.
M	Manifold	A device that connects two cylinders of a twin set together. It may contain its own 'isolation' valve in the middle.
	Maximum Depth	The deepest depth reached during a dive.
	MDT	Maximum Dive Time. The length of time that may be spent at a given depth without being required to make a mandatory decompression stop. Also referred to as No-Stop Time and Non-Decompression Time.
	MGR	Mixed Gas Rebreather.
	Mixed Gases	Any mixture of gas that deviates from normal (normoxic) atmospheric air.
	Multi Level Dive	A type of a dive that will not conform to a maximum depth and time profile. Ideally, such dives are conducted with the deepest sections first and then the diver ascends progressively to various shallower depths.
N	Narcosis	The intoxicating effects of breathing inert gases, such as Argon, Nitrogen or Hydrogen when the diver is exposed to elevated partial pressures at depth. The condition is generally alleviated upon ascending, or by changing the mixture ratios to reduce the partial pressure of the offending gas.
	Neon	A gas sometimes used in diving.
	Nitrogen	A gas that makes up approximately 78% of the air we breathe. It is usually the gas responsible for DCS when diving on compressed air. It also caused Narcosis from about 30m
	Nitrogen Narcosis	Loss of judgment and motor skills caused by the narcotic effect of breathing the nitrogen component of any breathing gas at elevated partial pressures (i.e. at depth). The condition is alleviated upon ascending. Also known as "Rapture of the deep" or "narcs". Nitrogen narcosis, a common form of inert gas narcosis, can be incurred at depths as shallow as 30m, and possibly even shallower by individuals who are more susceptible.
	Nitrox	Literally, any breathing gas consisting of a mixture of Nitrogen and Oxygen. Generically referred to when the Oxygen percentage in the mix is in the range of 21-50%. In diving,
	Normoxic	A breathing mixture that yields a partial pressure of Oxygen at normal (.21bar) levels.
	No Stop Dive	A dive in which there are no decompression or "offgassing" stops
O	Octopus	An extra breathing second stage for use in the event of a failure or an out-of-gas emergency with a diving buddy. They are usually coloured yellow.
	Off Gassing	The process of eliminating excess dissolved gasses from the body. The reverse of ongassing, more commonly referred to as decompression.
	On Gassing	As a person breathes air or any mixture of gases, a portion of those gases are absorbed through the lungs into the blood stream. Ongassing occurs primarily in the alveoli of the lungs (though it does occur at all levels, lungs, blood, tissues). This absorbed (or dissolved) gas is carried dissolved in the bloodstream and diffuses from areas of high partial pressure to areas of lower partial pressure throughout the various tissues (or compartments). As oxygen is metabolised it is "generally" not considered to be ongassing but does have limits as to how much can be absorbed safely. Excessively high partial pressures of oxygen can be absorbed and contribute to DCS, so ongassing as a term can be applied to oxygen. However, the partial pressures that can cause this are higher than those considered safe in relation to CNS O2 toxicity, so this is more an academic concern, rather than a real concern.
	Otitis	Otitis Externa - Inflammation of the external auditory canal due to infection. Otitis Media - Inflammation of the middle ear. This condition generally require treatment with antibiotics and may cause impairment of balance.
	Oxygen	A colourless, tasteless, odourless, non-flammable gas that accounts for 20.95% of the air we breathe.
	Oxygen Cleaned	Refers to the cleanliness of the system or component, or more specifically, the absence of contaminants. Contaminants vary but the most serious are those that act as a source of combustion such as oil, grease, paint, fingerprints, soot, lint, dust, metal particles, rust, cleaning solvents, and cleaning detergents. New SCUBA equipment is generally NOT oxygen clean.
	Oxygen Service	Refers to the suitability of a system or component for use in an oxygen environment. Oxygen service requires both oxygen clean and oxygen compatible components.
	Oxygen Toxicity	Short or long term physiological effects of elevated partial pressures of Oxygen. Also referred to as CNS Oxygen Toxicity.
P	Partial Pressure	The portion of the total gas pressure exerted by a single gas in a breathing mixture, expressed as Pg for an unknown gas or PO2 in the case of Oxygen.
	Physiology	The study of the body's actions and reactions. Diving physiology is primarily concerned with the effects of water pressure on the diver.
	Pillar Valve	The metal fitting on the neck of a cylinder. It consists of an on/off valve and a connection point for the regulator 1st stage.
	Pneumothorax	A lung over expansion injury that involves air bubbles escaping into the chest area and causing lung collapse. This can result from ascending to rapidly and/or breath holding.
	Pony Bottle	A small cylinder commonly used as an emergency breathing system, also known as a "Bailout Bottle".
	Poor Mans Trimix	Helium and Air
	Port	A connection for hoses on the first stage of a regulator. The first stage may contain 4-6 of these and they are usually marked with LP (low pressure) or HP (High Pressure).
	Pressure	Absolute Pressure - Absolute pressure is a measure of the pressure exerted on an object from all sources; includes water (hydrostatic) and air (atmospheric) pressure. Atmospheric Pressure -The measure of the weight of the surrounding column of air. At Sea level this is about One bar. Hydrostatic Pressure - The measure of the weight of the surrounding column of water.
	PSI	Pounds per square inch.
	Pulmonary Oxygen Toxicity	The cumulative effect (over time) of being exposed to Oxygen while the body is under pressure.
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R	Recompression	The accepted treatment for decompression sickness, CAGE and Lung over expansion injuries. Treatment is instituted by "returning" the diver to a higher pressure environment in a Hyperbaric chamber.
	Recompression Chamber	Hyperbaric chamber
	Redundancy	The concept of carrying fully functional backup systems to replace primaries in the event of failure.
	Repetitive Dive	Any dive following a previous dive within a particular time frame. This will vary according to the particular decompression model being used.
	Residual Nitrogen	The residual nitrogen (above normoxic levels) left in the body as a result of a previous dive.
	Residual Volume	The quantity of air remaining in the lungs after a forceful exhalation.
	Respiration	The voluntary or involuntary movement of gas into and out of the lungs and the associated metabolic process of oxygen and carbon-dioxide transfer.
	RIB	Rigid Inflatable Boat, commonly used by divers.
	RMV	Respiratory Minute Volume. The amount of air that is consumed in one minute on the surface. This is expressed in cubic feet per minute.
	Rule of thirds	A rule used primarily by cave and wreck divers that basically states that after having consumed 1/3 of your gas supply you should begin your exit from the cave/wreck. The remaining 2/3 of the gas supply is left for the exit, ascent and any emergency that may arise.
S	SAA	Sub Aqua Association. A UK based Diving club.
	SAC	Surface Air Consumption. The rate of underwater gas consumption converted to an equivalent surface rate, commonly measured in litres per minute. The average id about 25 l/min.
	Safety Stop	A procedure that calls for a making a safety stop at 6m for 1-3 minutes at the end of every dive for "degassing" purposes.
	Saturation	When a tissue has absorbed all of a given gas at a given depth that it can, it is considered saturated. The amount of dissolved gas a tissue can hold is dependent on the depth at which it is ongassing. The deeper the depth, the greater the amount of ongassing that can occur. As a rule it takes 6 halftimes for a tissue to become 99% saturated.
	SCUBA	Self Contained Underwater Breathing Apparatus.
	SEEDS	A BSAC pneumonic that can help to remember the components of a dive briefing. It stands for: S=Safety - safety aspects of dive e.g., currents, visibility E=Exercise - what the dive plan is E=Equipment - special equipment e.g., SMBs D=Discipline - leadership, positioning etc S=Signals - signals that will be used in the dive
	Shot Line	A rope attached to a heavy weight at one end and a buoy at the other. It is sank onto a wreck or other sea bed feature and used to guide divers.
	SMB	Surface Marker Buoy.
	Square Profile Dive	A type of dive that involves staying at one particular depth for the entire bottom time and then ascending directly to the surface.
	Squeeze	A pressure-related situation resulting from the failure to equalise on descent. Air-filled cavities such as sinuses, the middle ear, mask and dry-suits are the most commonly affected.
	Stage Bottle	Extra breathing cylinder carried in addition to the main gas supply. Usually carried on front or side mount clips, but may be attached to a decompression line. These cylinders are designed to provide additional bottom mix gas supply or to provide alternate mixtures for decompression efficiency.
	Staged Decompression	Decompression performed at specific depths where the diver remains for a period of time to offgas. This is the most common form of decompression for divers. Continuous decompression is generally not available to divers as it requires a very controlled continuous ascent, generally this is only available in a decompression chamber, or on dives that require only a minimum of decompression.
	Stop Dive	A dive which requires stops at certain depths for a set period of time. This is done on the final ascent and allows sufficient time to decompress.
	Surface Interval	The time from leaving the water at the end of one dive to leaving the surface on the next dive. A minimum of one hour is strongly recommended.
	Surfacing Code	The Code describing the degree of tissue saturation on surfacing from a dive. BSAC use A (no saturation) to G fully saturated).
T	Tables	These are tables from which you calculate how long and how deep you can safely dive and also details of any decompression stops you have to make on your ascent.
	Tachycardia	A rapid heartbeat of over 100 beats per minute.
	Technical Diving	A general term used to describe more advanced diving that requires the use of different gas mixtures.
	Test Pressure	The pressure to which a cylinder is taken to, during hydrostatic testing.
	Thermocline	A subsurface layer of water characterised by a rapid change in temperature and density in a narrow range of depth.
	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.
	Trimix	A breathing mixture of three gases, usually Oxygen, Helium and Nitrogen.
	Twin Set	A dual cylinder diving configuration. they may be ganged together or completely separate.
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V	Vis.	Short for visibility
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