Aqualung (aqua-lung) Aqua Lung is the name that first introduced the world to Scuba diving more than 60 years ago when Jacques-Yves Cousteau and Emille Gagnan developed the first "Aqua-Lung." By definition, it is a portable breathing apparatus for divers, consisting of cylinders of compressed air strapped on the back, feeding air automatically through a mask or mouthpiece, via a 1st Stage and Demand Valve.

Ascent Ascent is the physical movement from depth to the surface. Generally accepted as no faster than 18m (60ft) per minute with PADI, although virtually all dive computers are based on a 10m (33ft) or less per minute ascent rate.

Air Air is made up of approximately 20.95% Oxygen, O2, 78.08% Nitrogen, N2, .03% Carbon Dioxide, CO2, and .94% water vapor and trace elements or gases. For most non scientific purposes or applications, these values are rounded up to 21% O2 and 79% N2

Anoxia Anoxia is the end result of no oxygen (O2) reaching the bodies tissues. Death follows shortly.

Alternate Air Source There are four main types of Alternate Air Sources in two styles of system available. But all should be easily accessible not just to the diver him/herself, but also to their buddy. It is best if they are conspicuously marked, and it is suggested they are kept in a triangular area from the mouth down to your waist level. This facilitates ease of finding in an emergency. Also see

Alternate Inflator Regulator This style of Alternate Air Source is a second stage that is built into the Low Pressure Inflator (LPI) on one

Buoyancy Control Device aka BCD. Various designs and styles, but basically a unit worn similar to a jacket that is an integral part of of one's Scuba Unit. Used primarily to control buoyancy at depth, and to offer positive buoyancy on the surface.

Bottom Time Bottom time is the physical time spent underwater from the moment one descends, until one starts ones

Buoyancy Positive buoyancy is where an object displaces water more than its own weight. It floats. Negative buoyancy is where an object displaces water less than its own weight. It sinks. Neutral buoyancy is where an object displaces water equal to its own weight. It hovers in the water like a helicopter hovers in the air. Or a diver hovers on a reef wall.

Colour Spectrum The spectrum of colours that we have is actually made up of the seven colours of the rainbow. In order: Red, Orange, Yellow, Green, Blue, Indigo and finally Violet. As we descend under water we lose the red end of the spectrum first, then orange etc. This is why often depth looks a bluish colour. Carrying a torch by day or by night brings back the true colours to our eyes.

Delayed Surface Marker Buoy aka DSMB. A device used by divers at the end of a dive to indicate their submerged position to surface/boat cover. Generally "sausage" shaped, and inflated from depth and allowed to reach the surface, on a line. Used also by Technical Divers for the same reasons during decompression stops.

Dive Computer A computer used to monitor time, depth, NDL

Descent Descent is the physical movement from the surface to depth. To descend at the beginning of your dive.

Dalton's Law This states that the total pressure of a gas mixture is equal to the sum of the partial pressures of that gas. ie, in air at 1 ATA the PO2 (oxygen) is .21. The PN2 (nitrogen) is .79. The sum of those two gases equals 1.00 or 1 ATA.

Enriched Air Nitrox (EAN) Enriched Air Nitrox (EAN), is any gas mixture with more than 21% oxygen, O2, and the remainder is made up of nitrogen, N2. In nitrox diving, the standard mixes are usually 32% and 36% O2, (EAN32 and EAN36). The balance would be made up of nitrogen, N2.

First Stage (1st Stage) The valve the reduces the air in the SCUBA tank from high pressure, to an intermediate pressure.

Half Times The time it takes for a tissue compartment to become 50% saturated or desaturated with an inert gas (such as nitrogen, N2) is called a

Hypoxia This is a state in which lack of oxygen (O2) in the body tissues can lead to unconsciousness. Hypoxia generally starts at a PO2 of .16 ATA. It can lead to Anoxia. See Anoxia.

Invertebrate An animal without a backbone, (vertebrate)

Jacques-Yves Cousteau Jacques-Yves Cousteau was born on June 11, 1910, in Saint-Andr More information on: Jacques-Yves Cousteau

Nitrogen Narcosis Nitrogen narcosis or inert gas narcosis is a reversible alteration in consciousness producing a state similar to alcohol intoxication in SCUBA divers at any depth, but commonly beyond 30m. Jacques Cousteau famously described it as the "rapture of the deep". Its precise mechanism is not well understood, but it appears to be a direct effect of high nitrogen pressure on nerve transmission. The onset is hard to recognize, its severity is unpredictable, and it can kill, from its own toxic effect or due to the resulting illogical behaviour. However the cure for nitrogen narcosis is a simple one, as effects disappear upon ascending to shallower waters. source: http://en.wikipedia.org/wiki/Nitrogen_narcosis

Nitrogen (N2) An colorless, odorless, tasteless gas which makes up 79% of the air. Nitrogen is a gas at room temperature and becomes a liquid at about 77 K, -196

Nitrox Nitrox is any combination of Nitrogen, N2 and Oxygen, O2. See Enriched Air Nitrox, (EAN).

Normoxia The normal breathing of air with its oxygen PO2 at .21 ATA, sustains life. One can become unconscious at breathing levels of PO2 of .1 ATA. See Hypoxia.

Oxygen O2 O2. A percentage of the air we breathe. Generally held to be 21%.

PADI The Professional Association of Diving Instructors. PADI is the world's largest recreational diving membership and diver training organization. PADI Members (dive centers, resorts, educational facilities, instructors, assistant instructors, and divemasters) teach the vast majority of the world's recreational divers, issuing nearly 946,000 certifications each year. PADI professionals make underwater exploration and adventure accessible to the public while maintaining a high industry standard for dive training, safety and customer service.

Pony Bottle This is simply a small scuba cylinder and an independent regulator creating a redundant air source system for out of gas emergencies or unplanned decompression stops. A redundant air source system.

Regulator Any SCUBA device which changes air pressure from one level to a lower level. See "First" and "Second" stage regulator.

SCUBA SCUBA is an acronym for self-contained underwater breathing apparatus - a device (trade name Aqua-Lung) that lets divers breathe under water. Aqua Lung is the name that first introduced the world to Scuba diving more than 60 years ago when Jacques-Yves Cousteau and Emille Gagnan developed the first "Aqua-Lung."

Surface Marker Buoy aka SMB. Used by divers to indicate their position below the surface on drift dives, or to mark their position in area's of danger from boat traffic etc. Also see DSMB.

Second Stage (2nd stage) A value that delivers air, (or other mixed gases), to the diver at the ambient or surrounding pressure for any given depth.

Self Contained Ascent Bottle This is a small hand held cylinder that contains a small amount of compressed air, and can literally be

Thermocline The abrupt transition from one temperature of water, to another. Generally it is warmer water on the surface and cooler at depth. In colder climes though, one can find a

Visibilty aka

Vertebrate An animal with a backbone, (vertebrate)

Weight Belt Designed to counter act the positive buoyancy from an exposure suit. Many different designs and styles are available. Standard webbing belts, to soft lead pouches, to a braces design, to an integrated into your BCD design. All have a few things in common. They must have a quick release system/buckle to facilitate ditching in an emergency. They must be capable of carrying enough weight for the diver for that particular dive. The amount of weight is as variable as divers themselves. Thick neoprene suits or dry suits require more lead than someone wearing a shortie for instance. Plus as humans we are all different in our physical makeup. Therefore always perform a buoyancy check when moving from one environment/style/design of suit etc. to another.