| Phrase |
Description |
More info |
| A Run |
moving current |
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| A-clamp |
A type of pillar valve and first stage where the connection on the regulator surrounds the valve pillar and presses the output O-ring of the pillar valve against the input seat of the regulator. |
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| Absolute pressure |
Absolute or Ambient pressure is the pressure at a point for example on the surface we are subjected to 1 bar (1 ATM) of pressure from the atmosphere above us whilst diving we are also subjected to 1 bar (1 ATM) of pressure for every 10 metres of water we descend so at 20 metres we are under 3 bar (3 ATM) of pressure. |
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| Air Gun |
Attaches to a low pressure inflator and is used on lift bags . |
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| Ambient pressure |
See Absolute pressure |
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| Apeks |
A brand of Scuba Diving equipment. |
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| Aqua Lung |
A brand of diving equipment |
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| Archimedes Principle |
An object wholly or partially immersed in a fluid is buoyed up by a force equal to the weight of the fluid displaced by the object |
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| Barotrauma |
A Barotrauma is a pressure injury caused during descent or ascent. |
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| BC |
See BCD |
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| BCD |
Buoyancy Control Device - A piece of equipment in the form of a Jacket which provides buoyancy in the water |
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| Beauchat |
A brand of diving equipment |
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| Beaver Sports |
A brand of scuba diving equipment |
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| Boyles Law. |
According to Boyle’s law a flexible container will expand or contract in a precise relationship to the pressure surrounding it (depth) whilst at a constant temperature, This can be demonstrated by bringing a balloon filled at the surface to depth every 10 metres you descend the balloon is subjected to more pressure and so gets smaller (the volume is reduced) it will be half the size under 2bar of pressure (10 metres) 1/3 its size at 3bar of pressure etc. The reverse happens when rising to shallower depths the volume of the object will increases as it is subjected to less pressure. |
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| Bradycardia |
Bradycardia is the slow down of the heart and has been found to save near drowning victims in cold water for up to twenty minutes without breathing. |
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| BSAC |
A Dive Organisation - British Sub Aqua Club |
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| Carbon Monoxide Poisoning |
In diving carbon monoxide poisoning generally occurs from a compressor problem which overwhelms the filters. The reason that carbon monoxide poisoning is dangerous is that it binds with haemoglobin two hundred times better than oxygen, but does not unbond as easily. Once carbon monoxide enters your blood stream it can take twelve hours to eliminate it. Carbon monoxide is also colour and odourless. If unchecked carbon monoxide causes hypoxia (insufficient oxygen) Diving can further complicate this as at depth the tissues may get enough oxygen because of the pressure and the amount of oxygen you intake, but as you get shallow the pressure will decrease causing less oxygen bind because of the carbon monoxide and the diver blacks out without warning. Carbon monoxide poisoning may cause a persons lips and finger nails to turn bright red but it is rare. Physiologists have found that smoking can also raise normal carbon monoxide levels in the blood from three to twelve times. This can impair tissue oxygen transport and carbon dioxide elimination. |
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| Carotoid Sinus Reflex |
When the carotid sinus receptors detect high blood pressure, they stimulate the cardioinhibitory center, which slows your heart rate. When they detect low blood pressure they stop stimulating the cardioinhibitory center, which in turn regulates your blood pressure. The problem is that if you are diving with too tight a neck seal the cardioinhibitory center will be stimulated to slow your heart to reduce the blood pressure, as it is a neck seal problem it will keep thinking you have high blood pressure again decreasing your heart ate causing you to loose consciousness due to reduced blood supply to your brain. You would generally feel light headed first but you could eventually pass out if you ignore these symptoms. |
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| CFT |
Comhairle Fo Thuinn - Irish for the Irish Underwater Council |
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| Charles Law |
Charele’s Law differs to Boyle’s law in that Charles took temperature into account. Charles law states that the volume of a gas increases as the temperature increases as long as the pressure stays the same, likewise the volume decreases when the temperature decreases as long as the pressure stays the same |
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| CNS Central Nervous System Oxy |
In diving it is CNS Oxygen toxicity which concerns us most because we can reach exposures within the no stop limits. CNS toxicity can cause a diver to drown as it produces violent seizures under water which are then followed by gasps of breadth, this causes the regulator to be spat out and then water inhaled. Symptoms of CNS toxicity include visual disturbances like tunnel vision and blurring and ear disturbances like ringing and music, nausea twitching, irritability and dizziness (vertigo) This can be remembered by the acronym VENTID. |
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| Computer |
A electronic Device (similar to a digital watch) which calculates your dive profile by the use of algorithms |
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| Cylinder |
A cylinder is used in diving to transport gas (filtered air or alternative breathing mixes) to depth in order to allow the diver to breath from. The gases are under pressure allowing a greater amount of gas to be transported. Generally diving cylinders are under either 232 or 300 bar of pressure |
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| Cylinder Bands |
Cylinder Bands (also known as Tank bands) are used to twin tanks together and are metal straps which bolt the 2 cylinders together |
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| Cylinder Boots |
Cylinder or tank boots are rubber boots which slip over the end of the cylinder - They can aid in standing a cylinder upright, and help stop them slipping, although they can cause corrosion due to water being trapped and not drying etc, and are generally not used with twinsets etc. DIR divers generally remove them also as they are seen as a potential snagging point, wheras a rounded smooth cylinder is not |
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| Daltons Law |
The total pressure exerted by a mixture of gases is equal to the sum of the pressures of the different gases making up the mixture - each gas acting as if it alone were present and occupied the total volume. |
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| Dead Air Spaces |
Dead air spaces are located in the sinuses, trachea and bronchi, but with dive equipment extra dead air spaces exist in snorkels, regulators and full face masks. Dead air spaces are locations where excess carbon dioxide resides from the previous exhale and this is one of the reasons we are thought to take slow full breadths whilst diving |
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| Decompression Sickness |
Also called the Bends, A condition caused when gas bubbles form in the body after a dive. This is usually caused by a failure to properly ascend at a slow rate or properly use a computer or dive table. |
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| Decompression Stop |
A pause or multiple pauses during an ascent to a specific depth and time to allow the body to release dissolved gasses and avoid decompression sickness |
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| Din |
A type of pillar valve and first stage where the regulator screws into the pillar valve trapping the O-ring securely. These are more reliable than A-clamps because the o-ring is well protected. They are available in 232 and 300 bar versions. The 232 bar versions have 5 threads and the 300 bar versions have 7 |
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| Distance Line |
A reel ONLY used for line laying, for bad viz, finding your way back to the shot, exploring wrecks. |
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| Downstream Second Stage |
Second stages have two basic valve types. Downstream valves are most common. With these, when you inhale, the diaphragm pushes against a demand lever connected to a one way valve. This causes the valve to open, supplying you with air. Because the valve opens with the air flow, it’s called a downstream valve. Downstream valves have several advantages. First, they’re mechanically simple and therefore highly reliable. Second, the air flow pushes against them, so that they’re easy to set so they’re just barely closed. This makes it easy to breathe. Third, if a downstream valve does fail, it almost always fails in the open position. While this means your air freeflows, you can still breathe from it while ascending to safety. This is called a fail-safe design. |
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| Drysuit |
A waterproof suit designed to prevent a diver getting wet, two main types neoprene and membrane |
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| DSAT |
Dive Science and Technology Corporation. An Affilliation of PADI |
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| eRDPML |
eRDPML. (Electronic Recreational Dive Planner for Multilevel Dive Planning) A Dive Planner by PADI |
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| Fin |
A piece of footwear which aids the diver or snorkler to move in the water |
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| Garvin Hook |
This type of hook, allows a diver to attach a jon line to the shot line and it stays in place until the diver moves it. It is simple to use and operate, even with one hand. It will attach to ropes of various widths and release easily when required, but hold otherwise. It was named after one of it's two designers - Hank Garvin. Dan Berg was the other designer. |
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| Gas Narcosis |
Gas narcosis, nicknamed rapture of the deep, commonly called nitrogen narcosis because nitrogen is a primary culprit although other gases including argon, carbon dioxide and oxygen are equally or more toxic than nitrogen. Although people differ in relation to narcosis nitrogen narcosis is generally noticeable at thirty metres and below. Narcosis effects increased with depth affecting judgement, performance etc and is sometimes referred to as Martinis law where at thirty metres it is like having a martini and another for every fifteen metres or so. Drugs and alcohol can contribute to narcosis and conditions such as bad visibility, cold and stress although don’t seem to add to narcosis it makes it more noticeable and less manageable. |
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| Gauge pressure |
Gauge pressure is the measure of the pressure at depth not counting atmospheric pressure, so when on the surface your gauge reads 0 bar when it is in fact under 1 bar of pressure from the atmosphere. so at 12 metres the Gauge pressure would be 1.2 a.t.m.. |
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| GUE |
An organisation - Global Underwater Explorers (DIR Diving) |
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| Halftime |
Haldane assigned a halftime to each compartment, which is the rate at which it absorbs and releases nitrogen. |
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| Halocline |
A Halocline is the transition between freshwater and saltwater. |
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| Haskel booster pump |
Used to boost gas from nearly empty `J` type bottles. |
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| Heliox |
A mixture of Helium and Oxygen |
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| Henrys Law |
Henrys Law states that the amount of gas that dissolves into a liquid at a given temperature is directly proportional to the partial pressure of that gas. 2 primary factors affect gas solubility in liquids pressure and temperature. Basically it states that the gas will rush from an area of high pressure (where it already exists) to a area of low pressure (where it is non-existent or exists to a lesser extent) until both are at the same pressure. This is important as we consider the saturation of our tissues with nitrogen which will transfer from the air which we breed during the dive to our tissues, it is then during the ascent which causes the opposite to happen the gas will be released from the area of high pressure to an area of low pressure, which if we ascend too quickly may cause bubbles to form and may result in the bends. |
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| Hypercapnia |
Hypercapnia also called hypercabia is excess carbon dioxide within your respiratory and circulatory systems. |
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| Hypocapnia |
Hypocapnia also called hypocarbia or insufficient carbon dioxide is caused by either excessive voluntary or unintentional hyperventing. |
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| IANTD |
An organisation - International Association of Nitrox and Technical Divers |
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| Ikelite |
A brand of scuba diving equipment. Specialising in camera equipment and lights |
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| Indies |
Independant cylinders that make up a twin set. |
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| Isolation manifold |
This is a piece of equipment which allows you to connect two cylinders for a twinset. It enables you to gain access to the contents of both tanks through one regulator and read the total gas supply off one gauge. If you suffer a failure in one tank then you should normally still be able to gain access to the contents of both tanks through one pillar valve. If there is a worst case scenario, such as the failure of a main tank O-ring (highly unlikely) then you can "isolate" one tank from the other by turning a handle, which is in the middle of the manifold, this will protect half your gas supply. |
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| ITDA |
A dive organisation - International Technical Divers Agency |
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| Jon Line |
A length of rope or webbing used by divers to keep them in contact with a shot line but the diver doesn't have to hold on. Often used when decompressing in currents, or if there are too many divers who want to stop at that same depth on the shot line then you can use a Jon line to give you and the others more space by coming off the shot yet still not drift away. A Jonline often has a "Garvin Hook" on the side that attaches to the shot line. |
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| Knive |
A Knive is carried by a diver in the event of them becomming entangled in a net or wire etc. This would enble them to free themselves |
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| Lamp |
See Torche |
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| Lazy Shot |
A lazy shot is used for decompressing divers. It is like a short shot line that doesn't go down to the sea bed. The lazy shot is a rope with a buoy at the top to maintain buoyancy, it is attached to the shot line with a rope and clip at the start of the dive. At the end of the dive, the dive, the divers return to the shot line, then to the lazy shot. The last diver back to the lazy shot disconnects it from the main shot line. This allows the divers to decompress together whilst drifting in the current making their time more comfortable whist decompressing. The skipper now only has to watch for divers at one place in the water. As they are all together, there are more people at hand in case of an emergency, and spare decompression gas can be attached to the lazy shot at the appropriate depth. |
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| M Values |
The M value is the maximum tissue pressure allowed in the compartment when the diver surfaces, so as to prevent exceeding the maximum acceptable gradient. If the diver exceeds the M value in any compartment theres a risk of decompression sickness. |
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| Manifold |
A manifold allows two cylinders to be joined together for a greater supply of air or for redundancy of cylinder and equpment |
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| Mares |
A brank of scuba diving equipment |
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| NAUI |
A organisation - National Association of Underwater Instructors (NAUI) |
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| NDL |
No Decompression Limit - The maximum time you can stay at a given depth and still ascend directly to the surface without making a required decompression stop - Please note that a safety stop should however be performed on every dive. |
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| Neoprene |
A thick bouyany material used to create Drysuits, wetsuits, gloves and hoods. It is also used to protect and make some equipment more buoyant |
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| No Stop Limit |
Also called NDL The maximum time you can stay at a given depth and still ascend directly to the surface without making a required decompression stop - Please note that a safety stop should however be performed on every dive. |
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| Overhead Environment |
An underwater environment where the area directly above is not clear and open, hampering a direct ascent to the surface. |
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| Oxygen Toxicity |
There are two forms of oxygen toxicity Pulmonary oxygen toxicity from prolonged exposure to high levels of oxygen and central nervous system or CNS oxygen toxicity which leads to convulsions under water from high concentrates of oxygen due to being under high pressures. |
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| PADI |
A Dive Organisation - Professional Association Of Dive Instructors |
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| Pillar Valve |
A Pillar Valve is a mechanism which screws into the top of the cylinder and allows a first stage of a regulator to be screwed into it, There are a number of different types supporting different pressures |
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| Pilot valve second stages |
Second stages that have the diaphragm on the rear/bottom or on the side usually have pilot valves. With a pilot valve, when you inhale the diaphragm depresses a lever on a small valve. The small valve releases air pressure that in turn opens the larger main valve. The benefit of this design is that it provides greater airflow with less effort. The drawbacks to pilot-valve second stages include complexity and expense. They typically cost more and may be more difficult for service technicians to repair. Some users complain of a shallow-water phenomenon known as flutter. This is actually an awareness of the slight delay between when the pilot valve opens and when the main valve opens. This is less of an issue with the latest versions of pilot valve regulators. Pilot valves tend to freeflow easily, so most have a dive/predive switch. The predive setting puts tension on the diaphragm so it doesn’t |
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| Pony Cylinder |
A Pony cylinder is a 3-litre backup cylinder which can be carried either attached to your main cylinder or side slung from D-rings, If you should be in the unfortunate situation of suffering a gas failure in your main tank, then it should be adequate to get you back to the surface or to your buddy |
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| Pulmonary Oxygen Toxicity |
Pulmonary Oxygen Toxicity also called Lorrain smith effect is a form of oxygen poisoning that directly affects the lungs, unless ignored it isn’t usually a real concern and it is preventable by following established exposure limits. At forty metres it would take in excess of twelve hours for symptoms to occur. Lung irritation is the most noticeable symptom, but it may begin as a mild throat irritation followed by a cough, with more severe cases having a continuous burn in the chest. The body appears to recover when you return to normal levels. |
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| Ralf Tech |
A brand of diving equipment |
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| Refraction |
Refraction is a change in direction of light as it passes from one medium to another - in diving because of our maks and refraction objects appear 33 percent larger and 25 percent closer than they are |
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| Safety Stop |
A pause in the ascent usually at 5metres (15 feet) which is not required but made for added conservatism to further reduce the risk of decompression sickness |
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| Scrubber |
A canister in a Closed Circuit Rebreather which chemically removes carbon dioxide from the gas |
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| SCUBA |
Self Contained Underwater Breating Apparatus |
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| Scubapro |
A brand of Scuba Diving Equipment |
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| Sea & Sea |
A brand of scuba diving equipment. Specialising in underwater Photography |
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| Seac Sub |
A brand of diving equipment |
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| Silt Screws |
Used primarily in cave diving for a belay (attachment) point for line. They are generally made out of plastic pipe - 10mm - 50mm in diameter and 20cm - 60cm long. They have a 'point' cut in one end and a notch or loop of cave line in the other. The pointed end in pushed into the ground to provide an attachment point for the continuous line cave divers use. It not only gives them a belay point, but also keeps the line out of the silt. Though they are called silt screws, they can also be used in rocky places, or anywhere else that will hold to give a belay point and to keep the line out from areas you don't want it caught in. |
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| Silt Stakes |
See "Silt Screws" |
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| Slate |
Used for writing back up tables on & conveying messages |
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| SMB |
see Submersible Marker Buoy |
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| Specific Gravity |
Scientists measure whether a object will float or sink in a liquid as its specific gravity. Specific gravity measures the density of a given substance to the density of pure water. Pure water is considered the standard and therefore has a specific gravity of 1.0. Anything less dense than pure water will have a specific gravity of less than 1.0 and will therefore float, anything more dense than water will have a specific gravity of more than 1.0 and will therefore sink. |
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| Submersible Marker Buoy |
An Submersible Marker Buoy or SMB for short is a sausage like device which divers inflate and send to the surface. theese can be used to mark their location for boat cover, to aid safety or decompression stops and they also come in different colours which for example yellow ones may be used to inform cover of a problem below. |
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| Tank Bands |
Tank bands (also known as cylinder bands) are used to twin tanks together and are metal straps which bolt the 2 cylinders together |
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| TDI |
A dive organisation - Technical Divers International |
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| Thermocline |
A Thermocline is the transition between layers of different temperatures. |
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| Torch |
Similar to a torch used above water - A diving torch is obviously waterproof however and rated to a certain depth. There are numerous types and sizes of torches available according to the type and depth of diving undertaken |
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| Trapeze (Decompression Trapeze |
A device used for divers on decompression stops. It is a long bar (3m for example) or series of bars hung at different depths in the water e.g. 9m, 6m & 3m. They are attached to each other and have buoys at the top to maintain buoyancy. The trapeze is attached to the shot line at the start of a dive with a rope and clip. The divers come back to the shot and then subsequently to the trapeze at the end of the dive, and the last diver on the trapeze releases it off the shot line. This means that all the divers are together decompressing whist holding onto a stable bar. This helps the diver maintain the correct depth during decompression, it allows the skipper to only have to watch for divers at one place in the water. They can drift with the current making their time more comfortable whist decompressing. As they are all together, there are more people at hand in case of an emergency, and spare decompression gas can be attached to the trapeze at the appropriate depth. Should there be more divers than there is space on the bar, a diver can attach him/herself with a Jon line to the ropes on the trapeze, and still be with the group. |
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| Trimix |
Oxygen, Nitrogen and Helium. For a clear head at depth. |
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| Turbidity |
is the concentration of suspended particles in water rainwater runoff etc |
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| TUSA |
A brand of diving equipment |
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| Twin Set |
Twin-sets normally consist of two tanks they are used for allowing divers bring more air and for redundancy, Theese cylinders are joined together using a manifold, which gives the user access to both tanks through a single regulator, There are other ways of setting twinsets up, using different regulators per cylinder etc, each offering different advantages for equipment malfunction. |
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| UBA |
Underwater Breathing Apparatus |
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| Vasoconstriction |
Vasoconstriction is a constriction of blood vessels to reduce heat loss to the extremities of the body to help keep it warm. |
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| Visibility |
The distance you can see underwater |
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| Visual Reversal |
Visual Reversal results from the way your brain perceives objects being further away than they are because of clarity, contrast and the amount of light available in the water |
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| Viz |
The distance you can see underwater |
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| Weight |
Divers add weight to enable them to combat the buoyancy of their suits and equipment - this then enables them to descend below the surface |
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| Wing |
A device used to control buoyancy in the water. A wing fits be |
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