I love dive related stories, and I especially appreciate non-divers taking the effort to try and make the dive sequences as realistic as possible. You don’t have to pay any attention to this, I’ve done this to allow a little realism and correct terminology into dive related fiction for those that want it. This information is targeted at non-diver authors and is not a diver's resource (too much is missing to be of use to divers).

• Common diver jargon jumbles and technical mistakes in fiction
• Dive Environment
• Types of Dives
• Dive Procedures for Fiction
• Common Dive Equipment
• Diver Slang and Terms

Common diver jargon jumbles and technical mistakes in fiction

The number 1 mistake – Flipper was a dolphin, divers wear FINS.
Remember that… fins – always… never (ever) flippers. For example it makes more sense to say “there was a great white behind me, so I finned as hard as I could” rather than “there was a great white behind me, so I flippered as hard as I could” ... obviously “finning” means to kick your fins and move through the water. Divers do not use their hands to swim, usually the hands are folded close to the body (for a streamlined swim profile) or holding cameras / equipment and occasionally used to stabilise against a structure.

2. Ascent rates
It is paramount to suicide to have your diver make a rapid ascent to the surface. Divers do not do this (at least the ones that like to live) unless there is absolutely no other choice and even then it’s an act of pure desperation. The surface is not a diver’s friend. A safe ascent rate is 18m per minute or approx 1 foot per second. As a general guide you watch the little (slower) bubbles and go up NO FASTER than them. If your diver must make an emergency ascent, have them breathe out for the entire trip up. DO NOT have them hold their breath and kick for the surface. That = air embolism / lung over-expansion injury = death. They would be seriously ill, blowing foamy pink, blood tinged bubbles from the mouth and / or dead within minutes of reaching the surface if they held their breath on the way up.

3. Depth and bottom time
I won’t get into the details of depth, pressure and bottom time here, since its quite detailed information and generally not necessary for fiction writing - just remember that there are limits to how deep you can have your character go and how long they can stay on the bottom. The deepest scuba dive so far (a dive that took 10 years to prepare for) has been 313m (1010feet) using a mixture of gasses, and had a bottom time of about 12 minutes (bottom time is the time from the START of your descent to the START of your ascent… it does not count the decompression time. The decompression time (the amount of time to come back up safely) of that dive was 6 hours 40 minutes. At somewhere around 500m (1600feet) depth the human body will be crushed by the pressure but no one has got that deep to test it. In general and with a single tank, a diver will only go to a depth of 40m (130 feet / 22 fathoms). How long a diver can be underwater depends on the depth, how well they breathe, the volume and pressure of the tank (assuming a single regular tank here) and what they are doing. A "best case" example of a good diver at about 16m (around 53 feet) just hanging there and not doing anything physical, would have about an hour before running low on air or reaching the maximum amount of nitrogen absorbtion.

4. Regulator
A “reg” (or regulator) is the thing you stick in your mouth to breathe with. Remember that if for any reason this comes out of your diver’s mouth while underwater it must first be “purged” or “cleared” of water before they can breathe. It’s also acceptable to use the term "mask" for full face “tech diver” regulators where the regulator is built into the diver's mask. These masks can allow communication systems built into them and are used in shows like Thunderbirds. In general a mask refers to the bit over the eyes and nose. A diver can breathe fine without a mask – losing it isn’t going to drown them (although it’s hard to see and not very comfortable without one.)
It rarely comes up in fiction but the regulator has two stages. The first stage regulator is the bit that attaches to the tank (Usual term is “tank” or a “cylinder” - occasionally a “bottle”) the second stage regulator is the bit with the mouthpiece and there is a length of hose between the two. Note also that mouth pieces, can and do come out but they will not automatically fall out of the mouth if your diver becomes unconscious. When I first started diving, my buddy called me the knock-out queen because I knocked her regs out (a few times) – I don’t do that anymore. :P I only mention it to highlight the fact that the reg coming out of the diver's mouth is not a big deal. You simply recover it, put it back in, clear it and breathe.

5. Alternate air supply
All divers (apart from the already mentioned suicidal ones) dive with either a pony bottle or a buddy (the technical term for a dive partner is “buddy”) who has an octopus regulator. These terms are explained in the slang and terms section.
Unless your character is diving in a timeline set more than 20 years ago, (or for some reason they don't have octopus regulators in your universe) don't use the technique that you've probably seen in old James Bond movies where buddy breathing is done off a single regulator. The one where the regulator is passed back and forth between two divers. It's not done like that anymore... that technique had the unfortunate side effect of causing the death of one or both buddy divers. In a panic a diver tends not to give the reg back to their buddy. Fights would break out and sometimes neither diver would get the air. Now divers use alternate air supplies, such as octopus regulators, which is a fully functional regulator attached to the Buddy's tank. This alternate regulator allows both divers to breathe from the same tank(s). In an ideal world this should stop buddies panicking and fighting for the regs but in truth a frightened diver on the edge of panic will often grab the first functional reg they see... the one in their buddy's mouth. Fortunately at some point it usually occurs to one of the pair that the occy (octopus regulator) is there and all ends well.

6. Decompression and the Bends
This is a big topic and there are heaps of resources on the web about it, but for writing fiction purposes I’ll split it into the two topics and just give the basics.
Decompression.
Most recreational dives are done so that the diver does NOT reach the NDL (No Decompression Limit). Dives that exceed the NDL are decompression dives, which means the diver stops at various depths to allow the nitrogen to leave the body and prevent decompression illnesses like the bends. The NDL is calculated before the dive and/or during the dive if your diver is using a dive computer. The NDL is based on the depth of the dive and the length of time your diver is down there. Simply put, the deeper your character goes the less time on the bottom they have before the NDL.
For dives that do breach the NDL there are decompression stops. The number of stops and the length of each stop are dependant on the depth and time. I’d advise that if you’re writing a fiction with deep dives, talk to a diver. We have tables that help us calculate the exact “deco” stops but by just asking a diver you'll find out if what you’ve written seems realistic. If you can't find one my email is on this site... ask me. For fiction it doesn’t have to be perfect but it should be possible. If you had a diver go to 100+ meters and do a single 5 minute deco stop at 18m I’d laugh hysterically. Also be aware that a diver can’t (or should not) do a second dive that is deeper than the first. The time on the surface between dives is called a "surface interval" and is usually around and hour or two... anything less than 10 minutes is not realistic. It takes about 12 hours for the nitrogen to completely work its way out of the body tissues – which is why divers can’t fly in aircraft within 12hrs of diving… if they have done more than one dive or have done a decompression dive that time extends to 18hrs. Flying before the no-fly time expires can cause the bends.
The bends.
Commonly used and misused in fiction. The bends is just one type of decompression illness, other common ones that can be used in fiction are air embolisms and lung over-expansion injuries. Air embolism is when the expanding gas in the bloodstream actually blocks the blood flow. If this happens in the victim's brain it is a very serious injury. Lung overexpansion injury (pulmonary over inflation syndrome - POIS) refers to the direct effect of Boyle's Law on the human body when dealing with compressed gasses. Trying to put it simply... which is not easy.
Let's say your diver character is at 10 meters (30 feet) depth and fills his lungs with a breath of tank air. At that depth the amount of air in his breath is twice what it would be on the surface. Gas under pressure takes up less volume so he has to breathe more of it to fill his lungs. He is fine if he stays there or keeps breathing regularly while he changes his depth. BUT, should that diver fill his lungs and hold his breath then attempt to go up. The amount of air in his lungs begins to expand to its true volume. Our lungs are not designed to expand to twice their full volume so they rupture. Pink (blood laced) foam bubbles from your diver's mouth and he needs immediate medical attention or he may die. This is a lung over expansion injury.
As a rough guide every 10m (30 feet) of depth a diver will take another of the original volume into their lungs during a single breath.
So... on the surface 1 breath = 1 lung full (all is well)
10m (30feet) 1 breath = 2 lungs full
20m (60feet) 1 breath = 3 lungs full
30m (90feet) 1 breath = 4 lungs full.
So (hopefully) you will see that if your character is 40m (120feet) down which is the max depth for most divers he has 5 lungs full of air compressed in his lungs - he feels fine but to come to the surface with that will mean his lungs try to expand to 5X their normal size and he is dead.

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Dive Environment

What's it like underwater? How would you describe it in a work of fiction? The fiction is your work so I can't help you there, but what I can do is run through the senses and give a quick description. Humans don't have a lateral line so we can't sense electrical currents caused by muscle movement and heartbeat the way fish, such as sharks, do... mores the pity. What we have is:

Sight

Without a mask it's very hard to see anything at all, very blurry. It's also uncomfortable if you have bubbles passing by your eyes at each breath, and despite what you might think, water does not shoot up your nose but you can feel the water pressure. Some strokes (bad divers) and newbies panic when they loose their mask.
With a mask on you can see clearly, and because of the refraction of light through water, everything looks about 30% bigger than it really is... which means things look closer than they really are. It's common for a newbie to take a few swinging grabs at a line or anchor chain before they snag it.
The deeper you go the more colour you lose. The first to go is red... by the time you're 40m down (max depth for most divers) everything is in shades of blue and violet. By 100m the surface light no longer penetrates at all.
At a depth of anything greater than 20m, looking back to the surface the sun looks like a flare or burst of light and you can see distinct shafts of light. In shallower waters the waves cause ripples of light over everything... very pretty.

Sound

It's really hard to tell the direction of sound under water (for humans anyway) it seems to come from everywhere at once. Yes, there are sounds underwater, loads of them. If you try really hard you can even yell words and have them understood... but it's a waste of air, you're better off having your character use hand signals or write on a slate to communicate. You can hear your and your buddy's bubbles, clicks, hums, hisses, and the song of all sorts of marine life.

Smell

For a human there isn't any... moving on.

Taste

Well the taste of the water, obviously, but you can also taste the air you're breathing. Compressed air is cool. Good air only has a very, very subtle taste, but you can often taste it. Tanks are filled with everyday ordinary air... if there is a chicken shop next door to the dive shop where it was filled the air will taste of chicken. If air taste strongly or strange it's possibly bad and should not be used for diving. Your dive character can get seriously sick from bad air, which is sometimes a good thing. :D

Touch

You can feel the currents, water temperature and anything you touch. Your character might want to dive with gloves, there are a lot of sharp and stinging things in the sea. You can feel the pressure changes, most especially in the ears. You need to equalise the pressure in the airspaces of your sinuses. You pinch your nose and blow gently to correct it. To a lesser degree you feel the pressure change on ascent as well.
Hypothermia can be a serious issue when diving. Sometimes the temperature change (Thermocline) can be so defined you can literally reach your hand into water several degrees colder or warmer than the rest of your body is in.

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Types of Dives

• Open water -> Any dive where there is only water (no obstruction) between the diver and the surface, so that if the need arises the diver can head (at a controlled ascent rate) directly for the surface.
• Shore dive -> Dive entry to the dive site is made by walking backwards out into the water. Your character, no matter how coordinated they are, can't walk forward in fins though water, especially surf. Once deep enough they submerge and swim underwater, where the current is usually easier, to the dive site.
• Drift dive -> Usually, but not always, a boat dive as well. The dive starts at one point and the divers drift with the current and then end the dive at a different point to the entry. Usually the most relaxing and physically easy dives - unless it wasn't a boat dive because then you have to lug your heavy gear (and it is heavy) all the way back to wherever you parked the car.
• Boat dive -> Entry is made most commonly through one of three techniques (there are others) but usually it's a "giant stride", "roll forward" or a "roll back" look to the slang and terms section for definitions. Most often there is a non-diver who stays with the boat during the dive.
• Wreck dive -> What it sounds like. There are special considerations with wreck dives, such as getting light-locked, entangled, lost, milk or silt out, and getting trapped by collapsing wreckage or closing hatches that won't reopen. See the slang and terms section for definitions of most of these terms. Shipwrecks are often in deep water so many wreck dives are also decompression dives.
• Cave dive -> Many similar dangers to wreck dives but in a cave. Thermoclines can be more of an issue here... sometimes it gets very cold very fast in a cave. Currents can often be unpredictable and very strong. Divers should always have a continuous line or reel to the entry point so they can find the way back out again. This is also true in wreck dives, since it's easy to become disorientated. Mistakes and accidents still happen though so there is plenty of scope for a good story.
• Decompression dive -> A dive that exceeds the NDL (no decompression limit) in time, depth or both time and depth is a decompression dive. The NDL is calculated from tables which estimate the amount of nitrogen in the body tissues based on depth and time. In order to come up safely the diver must make decompression (deco) stops during the ascent. The decompression stops are usually planned in advance of making the dive. There is nothing to a deco stop... the diver just hangs in the water at the appropriate depth level, breathing normally for the required time before ascending to the next deco stop or the surface, whichever applies. Usually (good) divers will make what is called a safety stop even if they are within the NDL for the dive. A safety stop is a 3 minute decompression stop at 5m (15feet) depth.
• Square dive Vs Multi-level dive -> A dive where the whole dive is done at the same depth is a square dive (because of the shape of the dive profile map) and a multi-level dive is what it sounds like, a dive where different depths are visited. Multilevel dives are begun at the deepest point first then get progressively shallower... this decreases the amount of residual nitrogen. See the slang and terms section for definitions of most of these terms.

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Dive Procedures for Fiction

• Buddy breathing -> Unless your fiction is set in the early days of scuba don't use the method you've seen in James Bond films where a regulator is passed back and forth. This doesn't work out well. One diver may panic and stop sharing the reg, causing the death of the other. This is why Octopus regulators were invented, and nearly everyone dives with them now. In some countries you can't dive without one (or an alternate air supply of some type.)
• Hand signals ->
  Short distance diver OK - Circle forefinger and thumb, other fingers raised.
  Long distance diver OK - Used to tell the boat you're ok. Arm curled above head with fingers touching head, or both hands raised and joined to form an O shape.
  Tech / Military diver OK/salute - Raise forefinger. Should only be used if your character is this type of diver or wants to be recognised as such.
  Out of air emergency - Slashing motion across the throat
  Go up or go down - Thumb pointing up or down
  Lets stay at this level - Hand held flat
  Turnaround Time - Both hands held out into a T formation. Means time to head back and end the dive.
  Counting - System to count to 10 with one hand. 1 to 5 fingers pointing upright, 6 to 9 fingers (not thumb or it looks like the go up sign) pointing sideways then number 10 or 0 is a circle formed with the hand. (all fingers curled or it looks like an OK sign)
  Something's wrong - Hand held out, fingers spread and wagged from side to side (dipping the thumb downward then upward) followed by a point to what is wrong. For example if your character has noticed their buddy struggling to equalise and wants to ask if their ears are all right they would wag their hand, point to the buddy, then point to their own ear. This interprets to "something wrong... you... ears?" to which the buddy will reply with either an OK (interpreted as: "No, I'm fine") or a hand wag and a point to their ear (interpreted as: "Yes, something wrong... my ears.")
• Emergency ascent -> At all times try to have your character (assuming he/she is not a newbie) try to make controlled ascents but if the story demands the drama of an emergency ascent have the character breath out all the way to the surface. Never have them hold their breath to the surface or they will be dead from exploded (literally) lungs... a very messy way to die. Air expands as the diver rises so they will have the ability to breathe out for far longer than you might think. Divers are trained to "sing to the surface" You make a constant humming sound as you rise. The idea is that by doing this you may avoid the worst effects of lung over-expansion injuries and only have to deal with the traditional nitrogen bubbles decompression illness, "the bends" everyone has heard about. As soon as your character hits the surface they should attempt to inflate the BCD and get a snorkel in the mouth or get onto their back. This type of ascent can cause paralysis to come over the victim which can take effect before they are rescued from the water.
• Diver tows ->
  Fin push, where the injured diver is on his back and has his feet on your character's shoulders the character swims, pushing the other along. No good if victim is unconscious.
  Tired diver tow or tank tow. Have your character grab the tank valve and drag the victim by that.
• Panicking diver -> Don't have your character try to fight a panic diver... panic breeds panic, unless that's what you want to happen in your fiction. There are different techniques you can use to have your character subdue a panicking diver that will read true. If the action is happening at the surface have your character submerge (the panicking person will not go back under the water to follow) then come up behind the victim and grab the tank valve. Then your character can administer whatever first aid is needed. If under the surface have them hold the fin tips of a diver foolishly trying to kick to the surface. This gives them control and they can pull them down. Once again get your character behind them and grab the tank valve. From there they can pretty much control the other diver... unless he's insane and bails out of his BCD and tank.
• Buddy Check -> This is done between responsible buddies before getting wet. A simple check to make sure your buddy has all the gear in the right configuration and that the tank first stage valve is fully open (with a 1/4 turn back.)
• Lost Buddy -> What to do should be discussed between buddies before the dive, but in general if you lose your buddy you search for a short time (1 minute) leave a marker light if needed then reunite either at the surface or the first decompression point or the entry point (whichever is closest or applies)

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Common Dive Equipment

• BCD or BC -> Buoyancy compensation (device) is usually a vest worn when diving. it has air bladders in it that you can pump air into by pressing a button (autoinflator) on the low pressure inflator (you may have seen pictures of divers holding up a thick rubber hose and sinking into the water - that's the low flow or low pressure inflator) Take the air out of the BCD and you go down, putting air into it stops you descending and you can set your buoyancy to be neutral. Neutral buoyancy means you hang at the same depth. Negative buoyancy and you sink, positive buoyancy and rise. If your dive character has finished descending and is swimming around and for some reason is rendered unconscious don't have them either float up or sink down because they probably won't... they will just hang there.
• Weights -> You need weights to go down. Without weights you won't submerge and descend. Weights are either attached to a belt or are apart of (integrated with) the BCD. However the weights are carried there is always a method to quickly remove them. If your dive character is doing a dreaded emergency ascent, he/she will first "dump the weights" by releasing them and dropping them, this makes the diver positively buoyany and they will go up faster. Weights are also dumped at the surface if the diver is in a "left at sea" emergency to get their head higher out of the water.
• Dive knife -> The thing you DON'T kill sharks with... waving knives at them just makes 'em mad. Don't have your character try this, or if you do have the shark eat him. Knives are used to pry things loose or open and to cut away entanglements. Besides they look cool and you can fight the bad guy with them.
• Tank / cylinder / bottle -> Where the air be! Attached to the cylinder is a valve known as the first stage regulator. Generally from that you have 4 hoses,
  1 hose goes to the air pressure gauge so you know how much air you have left... a handy thing to know.
  1 hose goes to the BCD low flow connector so you and inflate the air bladder and control buoyancy
  1 hose goes to the primary second stage regulator where you do most of your breathing, and
  1 hose goes to the octopus second stage regulator in case your buddy needs air in a hurry.
• Exposure suit (wetsuit / drysuit) -> really don't need to explain this do I?
• Mask -> Dido here - sure you can work this out.
• Cyalume stick -> Those light sticks you snap and shake. If your diver is going anywhere dark they will have a light stick as a backup to the torch(s). Cave and wreck divers should be carrying 3 sources of light on a dive. One primary, one backup and one in case they need to leave a light marker.
• Safety Gear -> There is a lot of gear a diver can carry for safety, and I carry a selection depending on the type of dive I'm doing, but all divers should at the very least have a safety sausage (or signal tube). This is an eight foot long bright orange or yellow plastic tube. You fill it with air at the surface if you are separated from your boat. This way the boat will (hopefully) be able to find you.

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Diver Slang and Terms

The following slang and terms listing is by no means comprehensive and is meant to explain the more common and idiosyncratic terminology and slang to authors wanting their dive character to sound the part when sprinkled through a work of fiction and so non-dive writers will have some idea how and when to use the terms.

• Air hog or Hoover -> Someone who goes through their air fast. If you have an air hog for a buddy your dive will be over faster than you'd like. Sometimes you can use the term "Hoover" for a good diver. eg. "The great white was right behind me so I finned as hard as I could and hoovered my air."
• Bailout -> Either taking off or putting scuba gear on underwater - usually you enter the water with full gear and there is usually no reason to take it off during a dive but it is an emergency technique taught to all divers (or it should be) to handle certain conditions.
• Bent or got bent -> Term used to describe having, or having once had the bends.
• Bend-o-matic or Autobender -> Dive computers used by divers who do not plan the dive with tables before getting wet and jump in, putting all their faith (and lives) in the trust of the computer.
• Bounce -> The act of going up and down through various depth levels repeatedly. A repeat dive is sometimes called a bounce dive.
• Buoyancy -> In dive writing terms this is the act of controlling your depth altitude during a dive. For example "The young diver was so inexperienced he had trouble establishing buoyancy and kept sinking."
• Buddy -> There is a responsibility of care that exists between dive buddies and this should be reflected in your writing. Please don't have your character's buddy exist and then just vanish without your character either visually checking for them or at least wondering where they are.
• Chumming -> Puking underwater... most fun when done through the reg. Fish often magically appear to gobble up what you obviously didn't want.
• Dive Chick Vs Dive Babe -> If your diver character is a girl or has a girlfriend who dives they fall into one of two categories. A Dive Chick looks hot, complete with makeup done, and has her boyfriend prep her gear and carry it to the boat. It's not good to be a dive chick... sometimes called "princess." A dive babe is a female diver. Does her own prep and cares for her own gear, including lugging it around. Occasionally she looks hot but that's really hard to do as a diver so try not to focus on character looks while in scuba gear.
• Equalise -> The airspaces inside the human body are affected by the pressure changes of depth. Divers equalise the pressure by pinching the nose closed and gently blowing. Without equalising the pressure difference can cause intense pain and injury. Some divers have a great deal of trouble equalising and must descend slowly, stopping often.
• Freeflowing or gone free -> When a second stage regulator fails it's designed to fail so the valve is open. This causes the air to continuously flow through. Making lots and lots of bubbles. Tapping the reg usually fixes it, if not the air can be "sipped" from the reg and the dive should be aborted and a controlled ascent made. A free flowing regulator will go through your character's air very fast.
• Foul the hook -> Tie the wreckhook (an anchor with bendable tines) upside down to facilitate leaving the wreck. Usually done by the last diver up.
• Get wet -> Diving, an addictive action that really doesn't need explanation, only experiencing.
• Giant stride -> A Boat/jetty entry where you waddle up to the edge. Put one hand over your mask and the primary reg in your mouth and the other wrapped around any loose gear, then kick one finned leg out in a giant step and fall vertically into the water. Probably the most common dive entry.
• Goody bag -> A drawstring bag, usually mesh, where you put the fish speared or items you've collected from the dive site so you can easily carry them back to the surface.
• Halocline -> A barrier between two distinct layers of salt concentration... looks like a mist. Can affect the diver's buoyancy.
• Hang -> To float at a specific depth level for any period of time. eg "Peter was hanging at the 18m decompression stop when the great white appeared." Divers rarely say float. Float to a diver is a buoy.
• Incident pit or P.I.ed or clusterfuck -> A series or group of events that are not of themselves dangerous but when they happen in sequence or together put you in very deep, serious trouble. Been there, done that, no thanks.
• Lift bag -> A plastic bag... that looks like a garbage bag with strings or straps. The lift bag is attached to the goodybag or the item you want to take to the surface then air from one your regs is used to put a bit of air inside, just enough to make it positively buoyant. The diver lets it go and it goes to the surface for collection. They pick up speed on ascent as the compressed air expands.
• Light Locked -> Describes the condition when the diver (usually in a wreck dive) is unable to see a direct path out of the wreck.
• Looting -> Wreck diving for the specific purpose of taking things from the site.
• Milk out or Silt out -> Describes the effect of kicking up fine sediment in caves or wrecks and turning the water so cloudy that the vis (visibility) is reduced to zero. It's like swimming in milk. Sometimes the effect of careless or inexperienced divers but sometimes simply a result of the conditions. Danger is that in a cave or wreck it may become impossible to see the way out or even your buddy. Reason why wreck / cave divers use a line.
• Narced, Rapture or Rapture of the deep -> Nitrogen Narcosis. If you have to kill your character while diving, getting them narced is probably the most pleasant. Nitrogen narcosis doesn't kill them of itself but what it does is take away reason and rational thought. Divers make foolish decisions when narced, like deciding that they don't really need a reg to breathe after all. Occurs at depths > 30m. Diver becomes euphoric, disorientated, uncoordinated, exhausted and irrational. Divers generally have a few minutes when they can feel the sensation taking over and should ascend immediately. Even if the diver is not narced he/she will think measurably slower at depth.
• Nitrox or Enriched -> To dive deeper and or longer than 40 meters divers use enriched air which has a higher O2 content but there are dangers diving with enriched. Oxygen can become toxic under pressure. To prevent that in really deep dives another (inert) gas Helium is used (called trimix) but these are complex dives involving changing the gas mixtures. See Trimix.
• No-fly time -> The time period after diving when it is unsafe to fly in aircraft. 12hrs for a single, no decompresion dive, and 18hrs for either repeat dives or a decompression dive.
• Occy / Ocky / Octo or Octopus regulator -> The buddy alternate air supply. Divers carry Octopus regulators so that should their buddy have and out of air emergency they can easily share their air. Usually a highly visible colour like yellow for normal air and green for nitrox mix.
• Open water -> A dive or a point in a dive where the diver has a direct ascent route to the surface.
• Out of Air -> A dive emergency signalled between dive buddies by making a slashing motion across the throat by the calm, in control divers and by grabbing the working regulator out of the buddy's mouth by those less in control. Out of air emergencies happen fast and can cause a diver panic if they can't get to their buddy quickly and don't have a pony bottle. A buddy will share their tank air by either giving the diver in distress their octopus regulator (or using that themselves if their primary reg has been stolen) then doing a controlled ascent to the surface.
• Overhang -> Not an open water environment - There is an obstruction directly above the diver but there is a clear path to open water. The diver is not in an enclosed space.
• Penetration -> Not an open water environment - The diver is enclosed within a space. Penetration is mostly used in reference to wreck diving and the specific act of making a wreck entry and it's used as a way to describe a wreck. For example, "About halfway along the port side there's a penetration point, that leads you into the engine bay," Peter said.
• Pike dive -> A type of descent for those in a hurry. Pull the dump valve (a cord that allows all the air to leave the BCD quickly) then duck dive (turn upside down) and swim down. Sometimes used if you drop something off the boat and are playing fetch.
• Primary -> The usual regulator the diver uses. These tend to have more features than the octopus regulator like flow settings, but they are still basically the same thing - a second stage regulator.
• Pony or Pony bottle -> A totally independent alternate air supply. Like a smaller version of the tank and strapped to the diver's body, often the chest. The pony should have enough volume to get the diver to either the surface or a decompression tank.
• Purge -> (Second stage) Regulators have a purge button that allows you to squirt a little air through them to get rid of the water should the regulator be taken out of the mouth for any reason. You can also purge the water by just breathing out through it before trying to breathe in but that's usually termed "clearing." If you use the word purge, divers will assume you meant pressing the purge button so for continuity sake make sure the diver has a free hand.
• RNL or Residual Nitrogen Level -> After diving there is residual nitrogen left in the body which slowly works itself out. If a diver is going for a repeat or bounce dive the calculated level of nitrogen (RNL) needs to be factored into the next dive plan. Generally means the second dive is not as deep or is shorter than the first. The longer the surface interval the less the RNL and the less effect it has on the next dive. NOTE the repeat dive is ALWAYS planned to be at either the same depth or a shallower depth than the one before it.
• Roll-in -> Type of dive entry almost exclusively a boat entry. You either secure your gear and topple forward into the water - called a roll forward. OR more commonly sit on the edge of the boat, secure your mask with one arm (hand to the back of the head to protect from boat bumps) then roll backward into the water. Called a roll-back.
• Rupture or blow out -> What can happen to your sinuses or eardrums if you don't or can't equalise the pressure. Can cause paralysis and often bleeds like hell.
• Saturation Diver -> A whole type of diving I know nothing about. These are people who live and work at depth for long periods of time, for example deep water construction divers. Called saturation because their bodies absorb the maximum partial pressure for the various atmospheric gasses. This type of diving is very dangerous and hard on the body.
• Scuba -> Self Contained Underwater breathing apparatus.
• Sea spit or artificial spit -> Spit that comes in a bottle so you don't have to do anything as horribly disgusting as spit into your mask to de-fog it before a dive. Oh, the horror... only bought by divers who don't know any better.
• Slack water -> Time in a tidal area where the tide changes from in to out or out to in and at some dive sites it's the only time you can make the dive .. for example a cave entry or wreck penetration may only be safe in slack water. Pretty much it means still or no current.
• Shot Line -> A lead weight attached to a line and dropped over a dive site. for a night dive strobes are attached so the divers can find the way home.
• Stroke -> Either a diver so bad that they are dangerous to everyone or a diver that refuses to learn. Strokey is an action that is worthy of a stroke. Not to be confused with a newbie which is a newly certified or out of practise diver. Don't have your dive character string too many terms together or they will seem strokey... and using stroke too often is strokey too... as you can see.
• Sucked dry -> In diving this means to stay down too long, until you have reached the redline on your air pressure guage. Meaning you have sucked your tank dry. Not good.
• Surface interval -> The time on the surface between consecutive dives used to lower the residual nitrogen in the body but sometimes as a joke used to describe anytime that you're not diving... like Monday to Friday.
• Surge -> A type of current, an unexpected surge of current can push a diver into an obstruction or part of a wreck, but they can also be fun to play in.
• Swim Profile -> A good swim profile is a nice level, streamlined one with the hands tucked under or behind the body. A good swim profile makes it easier to move through the water, so the diver uses less energy, therefore the diver uses less air. If you ever watch Thunderbirds the diver in the show, Gordon, has a very nice swim profile considering he's a puppet!
• Swim-through -> An underwater structure large enough that a diver is able to fit through. Usually describes structures in open water dives where the diver is only blocked from the surface for a few seconds.
• Thermocline -> Sudden variation in temperature. Thermoclines can be so pronounced that the temperature can drop (or raise) several degrees in no distance at all.
• Trimix -> Gas mixture of three gases, Oxygen, Nitrogen and Helium. Management of gas mixtures needs to be handled carefully to avoid toxic reactions.
• Tox -> Carbon dioxide, Nitrogen and even Oxygen become toxic when breathed under pressure.
• Turnaround Time -> Before entering the water the diver(s) work out a safe turn around time. This is usually not a time at all but a pressure on the air gauge. The first person to reach the nominated pressure signals time by making a T shape out of their hands then the divers begin to head for the exit point.
• Vis -> Visibility. The distance in meters or feet that you can see in any unobstructed direction.
• Zero vis or Braille dive -> When the visibility is so bad you can see less than a meter. It's very easy to lose your buddy in these conditions and if in a cave or wreck without a hand on a continuous line back to the exit a diver may become hopelessly lost and trapped.

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