Diving Terms and Definitions

In order to give credit where it's due, though I did not go and read their definitions to write mine, much of these definitions may be similar to what was listed in the book I learned from:

Open Water Diving Manual; Scuba Schools International; Fort Collins, CO; September 1998.

Injuries/Illnesses and Related Terms - Terms, Tools, Techniques, and People - Underwater Equipment

Injuries/Illnesses and Related Terms
Decompression Illness or DCI	The name given to most decompression related injuries, such as Decompression Sickness or Overexpansion Injuries, since the symptoms for these illnesses are much the same (I've written a page that tries to explain the finer points between the two, particularly for those who would like to be able to diagnose them with some accuracy). First aid for all decompression illnesses is the same: basic first aid (often called the "ABC's" - Airway, Breathing, Circulation); give them 100% oxygen; and get them to a hospital. The Diver's Alert Network (DAN) should be contacted; in the event that the patient needs to be recompressed in a hyperbaric chamber, DAN will be able to provide information regarding the closest health care facility with a hyperbaric chamber.
Decompression Sickness or DCS or "The Bends"	As you descend on a dive, you require more air (at the same volume but a higher pressure) to breathe. The oxygen in the air is used as your body usually would use it under normal circumstances. However, the excess nitrogen in the air is absorbed into your body tissues. As you surface, this excess nitrogen, under ideal circumstances, comes out of 'solution' with your blood and body tissues and exhaled normally. However, if a diver surfaces too quickly, or does not breathe properly as they surface, the nitrogen expands to form bubbles in the body tissues or blood stream. Bubbles in the joints cause much pain, and often cause the victim to bend over (hence the slang term, "The Bends"). Other symptoms range from skin rashes to paralysis (and death, if not properly treated). A "DCS hit" is a (slang) term for the suffering of DCS symptoms; an "undeserved hit" is slang for the suffering of DCS when the victim did not violate normal diving protocol, particularly in regards to dive tables/computers and ascent rates (as in "He suffered what they thought was an undeserved hit, but his dive computer reported that he surfaced too quickly").
Hyperbaric Chamber or Recompression Chamber	In order to appropriately recover from a decompression illness, it is often required that the victim undergo recompression, simulating the physical pressures that the body is under when at depth. Although there are probably other medical reasons for the need to put the victim under pressure, the obvious one is so that any gas bubbles trapped in the body can be forced into a state to where they can be safely removed from the body. Since this is normally done through a slow ascent rate and regular breathing, this must be simulated. Instead of using water and an air tank, the chamber uses pressurized air (and I would guess that the oxygen content in the air is probably slightly higher than normal). From the victim's stand point, visits can be inconvenient to say the least, and rather expensive; also, more than one visit may be required for recovery from a decompression illness. I've heard that many insurance policies may not cover visits; one would be advised to investigate obtaining dive insurance through DAN.
Nitrogen Narcosis or "Narced"	A danger that can occur when divers reach deeper depths (for some, lower than 80 feet, for most, below 100), it is characterized by a loss of cognitive ability and dexterity. Sometimes described as being similar to being drunk; witnesses have described divers as being confused, swimming away in the wrong direction, even laughing through their regulator. It is important for divers to recognize the onset of narcosis symptoms in themselves and their buddies; the solution is usually to just ascend until the symptoms go away, and not proceed to the depth where symptoms were experienced. One dive instructor provided the suggestion that a clue that one is suffering from mild narcosis symptoms is when one looks at their gauge, and after letting it go, one cannot remember what they just read from the gauge.
Overexpansion Injury	As a diver surfaces, any air in the lungs begins to expand. If a diver is not breathing normally and exhaling properly, the expanding air can cause the aveoli (the sacs in the lungs that allow oxygen to pass into the blood stream) to rupture and release air into the blood stream or other areas of the body. Much like DCS, overexpansion injuries can cause anything from skin rashes to death. Different kinds of gas embolisms (which are marked by different kinds of symptoms) are the result of overexpansion injuries.
Oxygen Toxicity	Fully termed "Central Nervous System Oxygen Toxicity," it is a condition that can occur at high PPO₂ levels, particularly if the high level is experienced over a longer time. Symptoms of oxygen toxicity include convulsions, blurred or tunnel vision, tinnitus (ringing in the ears), nausea, muscle twitches, and dizziness. Though not usually life threatening on land, convulsions under water can cause a loss of the regulator from the mouth, resulting in drowning.

Terms, Tools, Techniques, and People
C-Card or Certification Card	Your C-Card, or Certification Card, shows that you have completed at least a basic Open Water dive course and are therefore certified to dive. Any reputable dive shop, boat, or location will not allow you to dive without seeing your C-Card. SSI provides different levels of C-Cards for different levels of instruction (OW, Advanced OW, Stress and Rescue, Dive Con, Instructor, probably more). Keep it with you whenever you plan on diving, or you may not actually be able to dive that day!
DAN or Divers Alert Network	The Divers Alert Network, or DAN, is an organization that provides services to its members that includes education, diving insurance, and diving information. DAN is also a research organization, helping to extend the collection of knowledge that exists regarding diving. I have been told that insurance purchased through DAN is "total coverage," including recompression chamber fees. DAN also maintains hotlines for medical information and diving emergencies. DAN members gain many benefits for a small fee, including the insurance, which is very low cost (though it only covers dive related situations). Any diver that dives regularly would be wise to consider becoming a member of DAN.
DiveLog	Your dive log contains information about the number of dives that the diver has done. It can detail date of dive, buddy's name, where the dive was, what the weather was like, what the water was like, what you had for equipment, and the dive plan, which outlines any residual nitrogen for computing multiple dives on the same day. A diver should also consider providing a narrative (which for SSI is on the back of your typical divelog entry) which states in the diver's words what the diver saw, what (if anything) went wrong, and how the diver could become a better diver.
Dive Tables	Dive tables are used to plan safe, no-decompression, recreational dives. The tables take into account time at a certain bottom depth, residual nitrogen in the body due to previous dives, and any time spent not diving between dives. Images of SSI's dive tables can be seen to the right. SSI uses three separate tables; some organizations combine some of the tables. Table One is a depth versus time table, used to determine an 'arbitrary' letter rating (Group Designation, or GD) which represents the amount of residual nitrogen left in the body after a dive. Table Two is used to determine the change in GD dependent on the Surface Interval Time (SIT), the time spent at the surface/out of the water. Table Three is a depth versus residual nitrogen table, which gives two numbers: the Residual Nitrogen Time (RNT), the time added to your Actual Bottom Time (ABT) that results in the Total Bottom Time (TBT) for your next dive; and the maximum ABT that can be safely spent at that depth, given the body's letter rating. As a short example, let's say during a dive I go no deeper than 56 feet, and the time from when I start my decent to the time I start my ascent is 23 minutes. According to Table One, my GD is: E (always round up; 56->60, then go over to 23->25, and then follow the column down to the letters). I stay out of the water for two hours (my SIT, which must be at least 10 minutes; anything less is considered a continuation of the previous dive). According to Table Two, my GD is now: C (follow the column down of your original GD, then move across until the SIT falls between the indicated times, then follow the column down to the new GD). Table Three says that as a C Group Designation, I can spend no more than one minute at 120 feet (that one minute starts as I begin to decend from the surface and start to ascend to the top...it would probably take me longer to get to 120 feet) and that however long I spend down there, I must add 9 to that time to get my Total Bottom Time. I plan my dive for: 55 feet (round up to 60) and no more than 20 minutes (according to the table I can only have an Actual Bottom Time of 33 minutes at that depth, and must add 17 to my ABT) down. As it happens, I end up spending 22 minutes as an ABT (but at least I went no deeper than the planned 55 feet); I add the 17 minutes of Residual Nitrogen Time and get a Total Bottom Time of 39 minutes. Now I go back to Table One. With a TBT of 39 minutes at 55 feet, my GD is: G. Now I start all over again. Tables are designed to be conservative, and are read conservatively; so that even if you only spent 1 minute of your dive at your maximum depth, you still read the table as if you spent all of your ABT at that depth. You also always round up. Dive Computers can extend your dive times as they take into account time spent at different depths during the dive (at a minimum; some even monitor your oxygen intake and breathing rate). Diving and violating the tables is a bad thing; the risks include DCS or other decompression illnesses. Recreational Diving is meant to be done with no decompression stops (except for what is considered a 'safety stop' of five minutes at 15 feet). Even after the example, if you don't understand dive tables, don't worry...it takes a lot of practice and I personally still get them wrong from time to time. During any open water dive class that you take, you will most likely receive lots of instruction on dive tables in particular, and probably a test with many dive table questions.
Equivalent Air Depth or EAD	A term from Nitrox diving. Used as an alternative to using specially prepared Nitrox tables, a diver can use the Equivalent Air Depth equation to calculate, given the percentage of nitrogen in a gas mix, the theoretical depth experienced had the diver been diving on regular compressed air. The result of the equation is a shallower number that can be applied to standard air tables when planning a dive. It is important to remember that the equation wants the percentage of nitrogen, not the percentage of oxygen (which is what is usually referred to in Nitrox diving). The equation is as follows (depth is considered fsw): {[(N₂%/100)/.79] X (DEPTH + 33)} - 33
ffw	Simply, "feet freshwater". In rare cases, it can make some difference if you are diving fresh- or saltwater.
fsw	Simply, "feet saltwater". In rare cases, it can make some difference if you are diving salt- or freshwater.
Maximum Operating Depth	The calculated depth at which a particular mix of Oxygen and other gases (usually just Nitrogen) will reach a PPO₂ of 1.6 (or, for more cautious divers, a lesser value such as 1.5 or 1.4). It is the depth at which even short term exposure to the increased PPO₂ can be toxic, resulting in Oxygen toxicity. The maximum operating depth of a particular mixture of Nitrox should be determined before diving with it. Many dive shops that fill Nitrox cylinders make the diver sign off on both the O₂ percentage of the mix as well as the maximum operating depth for a PPO₂ of 1.6.
Nitrox or EANx or Enriched Air Nitrox	The term "Nitrox" technically applies to any mixture of O₂ and N₂ (Oxygen and Nitrogen). Standard "Air" mixes are usually 21% Oxygen, 79% Nitrogen. However, the term "Nitrox" in the dive community is often used to refer to mixtures of gas that have a higher percentage of Oxygen than the standard 21%. Common mixes include 32% and 36% (often, the "EANx" abbreviation has the numerical percentage replacing the "x," such as EAN32 or EAN36) Oxygen (and 68% and 64% Nitrogen). In theory (and usually in practice), the inclusion of a higher percentage of Oxygen results in less Nitrogen going into solution in the body tissues at depth, thereby reducing the chances of Decompression Sickness. The result is a longer bottom time for a given depth (most noticeable at depths between about 40 and 65 feet) and the benefit of shorter SIT times. The trade off is that at deeper depths, the higher percentage of Oxygen can become toxic to the body, causing convulsions that lead to drowning (as an example, a good portion of the dive community opines that 100% Oxygen can become toxic at depths deeper than 20 feet). The Maximum Operating Depth of a mix is computed using partial pressures of the Oxygen at a given depth.
Partial Pressure of Oxygen or PPO₂	The amount of oxygen at a given depth in terms of pressure. At sea level, the amount of oxygen in terms of atmospheres in normal air is 0.21. As a diver goes deeper, the pressure the diver's body experiences increases one ATM every 33 feet (so that at 99 feet, a diver is under 4 ATMs of pressure). To determine the the partial pressure of oxygen, multiply the percentage of Oxygen in the mix by the ATMs of pressure for that depth (standard air at 99 feet has a partial pressure of Oxygen of 0.84. The partial pressure of Oxygen becomes a concern particularly when diving on Nitrox, as high PPO₂ levels can increase the risk of CNS Oxygen Toxicity. The partial pressure of Oxygen in a mix of Oxygen and Nitrogen should under no circumstances violate a value of 1.6; according to this rule, even standard air becomes toxic beyond 218 feet. Taking this value of 1.6 and computing the depth at which a particular mix of gas reaches this value gives you the Maximum Operating Depth for that mix.
Surface Interval Time or SIT	The time from the end of one dive to the next. Most (if not all) dive organizations require this time to be a minimum of 10 minutes long; otherwise, the "next dive" is considered an extension of the first (the times are added together). Most dive computers also consider a SIT of less than ten minutes insufficient and just continue reporting the "second dive" as an extension of the first. Most divers use this time to snack and drink water (dehydration can contribute to the chances of a DCS hit).

Underwater Equipment
Air Tank	The air tank holds the compressed air that is breathed while under water. Usually the air is standard 80% nitrogen, 20% oxygen, but it can also contain Nitrox mixes. The air tank is strapped to the BC. Valves at the top of the tank (either DIN or USA Yoke/K valve type) connect the air tank to the First Stage of the regulator. Air tanks are made of either steel or aluminum, and usually come in one of four sizes: 63, 80, 100, 120 cubic feet. They usually hold air from 2250 to 4400 psi when full.
Buoyancy Compensator or BC	A device worn like a vest, that helps the diver become neutrally buoyant. The BC also holds the air tank (on the back). BC's also can hold weights (often termed a "weight integrated BC"). They usually have clips for various equipment, including the octopus and gauges. BC's have air bladders (either on the back or the sides under the arm pits) that can be filled usually by air from the air tank. While descending, air is pumped into the BC only to maintain neutral buoyancy (you actually become less buoyant as you dive deeper). Air is almost never pumped into the BC while surfacing.
DIN valve	Used for tank pressures over 3000 psi, DIN stands for Deutsches Institute for Normung. It only recently started becoming popular in the U.S. The First Stage of the regulator connects to the valve of the air tank.
Dive Computer	An electronic device that often takes the place of one or more of the regular gauges. Dive computers can simply monitor depth and air tank pressure (either through a tube connected to the First Stage of the regulator, or through a transmitter mounted on the First Stage). More complex dive computers can store dive history, compute more accurate body nitrogen content (often displaying how long the diver has been under water, how long the diver has been at a particular depth, and warning when to start the ascent to keep the dive a no-decompression dive), display ascent rate, beep when air gets low, and even (should the need arise) at what depths and for how long to do a decompression stop.
Dive Skin	A thin layer of protective clothing that provides some protection from cool water and sea life. Also often worn under a wet suit to provide more warmth. It is also easier to put on a wet suit over a dive skin.
Dry Suit	A protective underwater outfit, usually used in cold weather. Water is prevented from entering the suit and contacting the skin.
First Stage	Part of the regulator, this part connects to the actual air tank and reduces the airflow to an intermediate level. All the tubes for the gauges or dive computer, Second Stage, BC, and octopus hook into the First Stage.
Gauges	There are usually two gauges: a depth gauge (that tells how deep the diver is, and usually contains a marker noting the deepest depth reached), and the pressure gauge (which shows how much air is in the air tank).
O-Ring	When referred to by itself, the term "o-ring is usually referring to a small rubber gasket, used on USA Yoke valves, that ensures a good seal between the valve and the First Stage. The phrase "Blowing an o-ring" usually means the loss of an o-ring, either under water (a very bad thing, since your air stops to function properly, and starts to leak out at an extremely high rate) or on the surface (occasionally due to the incorrect disassembly of the regulator and the valve). O-rings usually do not blow under water unless the o-ring is damaged. Part of the assembly of an air tank with a USA Yoke valve, regulator, and the BC should be a thorough check of the o-ring's condition (or at least it's presence since as far as I know you can't dive without one). The o-ring should be free of cracks or dryness. Every diver who uses USA Yoke equipment should have spare o-rings of varying sizes in their repair kit. You will also hear the term "o-ring" used to refer to any rubber-like gasket that ensures a water-proof seal on dive equipment (IE, dive computer battery compartments, camera housings, etc).
Octopus	The nickname for a secondary or backup Second Stage, it is usually colored bright yellow, or some similar high visibility color. Used if the primary Second Stage fails, or as an alternative to Buddy Breathing, so you can more easily share air with your Dive Buddy. Pictured is an Integrated Octopus, which contains controls for B.C. inflation.
Regulator	A regulator has two parts, the First Stage and the Second Stage. A regulator reduces the flow of compressed air from the air tank to a useable/breathable level.
Second Stage	The part of the regulator that actually goes into your mouth. Reduces the flow of compressed air from the First Stage from an intermediate to an 'ambient' level, making it easier to breathe under pressure. The Second Stage is designed to deliver the air to match the pressure of the water around the diver.
USA Yoke or K Valve	Used on tanks to a pressure of 3000 psi. It's been said that the name K Valve is from an old Sears Catalog, when more than one valve was sold. There was a letter listing for a valve under j, and a letter listing for a valve under k. The valve that was listed under j is reportedly no longer used, but the "K" valve is (and is also known as the USA yoke). The First Stage of the regulator connects to the valve of the air tank. USA Yokes require an O-Ring.
Wet Suit	An exposure suit, made of neoprene, of varying thickness, that insulates a diver from cold water. A full wet suit is suggested when the water is between 65 and 75 degrees. Wet suits work by allowing some water in between the wet suit and the diver's skin. The diver's body then warms up the water but the wet suit keeps most of it in, not allowing it out. This keeps the diver warm. Loose fitting wet suits will allow the water to circulate out and prevent the water in the wet suit from warming fully. A tight fitting wet suit will not allow enough water in for the body to warm appropriately. Water draws heat from the body roughly twenty-five times faster than air of the same temperature, which is why water at 77 degrees feels much colder than air at 77 degrees. Pictured is a "Farmer John" (since it looks kind of like overalls) and a Shorty. Farmer Johns are usually worn with a Shorty.

By Eric Stewart - The Dive Log - Blog - Mastodon
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