Last Updated on June 21, 2024 by Steve Weinman
While learning how to dive, you’ll probably notice that there are a lot of TLAs in the scuba-diving language. TLA is a Three-Letter Acronym. SCUBA is an acronym itself: Self-Contained Underwater Breathing Apparatus. A firefighter’s breathing equipment is called an SCBA – they just remove the underwater part.
You’ll probably hear a lot of acronyms around the dive-centre, dive-sites and in online forums. Here’s your chance to brush up on as many TLAs as possible (it works for a two-letter acronym too).
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BCD
Starting off with BCD, this is one of the very first acronyms that most divers think they know when they learn how to dive. But you’ll really annoy some divers when you say the wrong thing. They take it quite personally that you call it a Buoyancy Control Device. It’s not a Buoyancy Control Device – it’s a Buoyancy Compensating Device or a Buoyancy Compensator (and that, incidentally is what it’s always been called here on Divernet – a BC).
SMB
Your SMB is your Surface Marker Buoy. These are usually bright red inflatable buoys that you tie to a string and then tow around during the dive from beginning to end to mark your location and let boats in the area know that you are down there. But try not to get them confused with a DSMB, which is a Delayed Surface Marker Buoy. A DSMB comes down with you on the dive, deflated, in a pocket or clipped off to a D-ring. At the end of the dive, you inflate it, attach it to a spool, and it shoots up to the surface, letting boats know that there’s a diver in the water nearby.
EANx
EANx or EAN is Enriched Air Nitrox. When filling up cylinders, we add air and then a bit of pure oxygen, or sometimes we use a membrane to increase the amount of oxygen inside the cylinder, which can help to extend our bottom time.
LPI
Low Pressure Inflator. If somebody refers to their LPI, it’s going to be the inflator on their BCD or sometimes their drysuit or any other equipment that might need inflating. It’s fed from an LPI hose. We don’t really use LPI hose as a single syllable word, so it’s just as easy to say LPI.
DIN
DIN stands for Deutsche Institut für Normung. It means the German Institute for Standardisation, because Germany has an institute for standardising everything. DIN isn’t strictly the correct term for this because this is also a DIN fitting. This on your regulator is actually a G58 thread. It’s commonplace that we call it DIN – sometimes an M26 if you want to get really technical – but DIN is fine.
SPG
Your Submersible Pressure Gauge. It is surprising how long it took before divers could actually see how much gas they had in their cylinder during the dive. They just didn’t dive with gauges but, eventually, a submersible pressure gauge was produced. Pressure gauges were not new but ones that could be taken under water were. We still call them SPGs.
RDP
You might not see many of the next few thanks to dive-computers and updating training standards, but RDP is your Recreational Dive Planner or dive-tables. RDP is quite specific to PADI; it’s what it named its dive-tables. Each training agency uses its own dive-tables. Dive-computers have reduced the need for tangible dive-tables, which is a bit of a shame. If you didn’t learn your tables, it’s worth checking them out and learning how to use them.
NDL
NDL is your No Decompression Limit, which is simply how long you can stay at a given depth and then return to the surface without requiring a decompression stop. Most training agencies train you to complete a safety stop at the end of every dive where you hang at 5m for three minutes. A deco stop is like that, but the depth and time might vary, and they’re not quite as optional.
RNT
Residual Nitrogen Time: When you complete a dive and are back on dry land, you still have some nitrogen inside your body that you’ve absorbed at depth. When using dive-tables, you need to work out how much nitrogen is still in your tissues. Your residual nitrogen time is a theoretical amount of time you work out with the tables and add to the next dive time for your next dive. Your dive-computer does this for you if you’re diving with one.
MOD
MOD is your Maximum Operating Depth. It’s more about the gas you’re breathing and at what depth that gas becomes dangerous to breathe. When you start diving different gas-mixes, you’ll see stickers and markings on cylinders denoting their maximum operating depth, or how deep you can take them.
AAS
Alternate Air Source. It’s your second second stage. We all dive with at least two second stages, and the one from which you’re breathing is your primary, and the other is your alternate. Some divers call it an octopus or octo, but some divers will call it an alternate. (Strictly speaking it should be ‘alternative’ in non-American English, and usually is on Divernet)
CCR
Closed-Circuit Rebreather: If the diver is blowing bubbles with every breath, then it’s an open-circuit regulator because it’s an open circuit. We have equipment that can recycle the exhaled gas that we breathe by scrubbing out the carbon dioxide and topping up the oxygen in a closed loop. That’s called a Closed-Circuit Rebreather or CCR.
BOV
Bail-Out Valve: Normally in the form of a lever or switch on the mouthpiece to swap between closed-circuit and open-circuit second stage. It’s built into the mouthpiece so you don’t need to remove the mouthpiece to change from your rebreather to a more traditional open-circuit second stage.
DCI + DCS
DCS or Decompression Sickness refers to a variety of ailments from nitrogen bubbles forming in your body and causing local damage. If a bubble forms in an artery, it can block blood-flow and cause an Arterial Gas Embolism or AGE. DCI or Decompression Illness covers both DCS and AGE. DCI is a more all-encompassing term.
DIR
DIR or Doing It Right, or sometimes Diving It Right, is a specific approach to diving to maximise safety. DIR isn’t a training agency; it’s a holistic way of assembling your equipment and diving, developed by a team of divers to explore cave systems and dive very deep and long dives. They evolved DIR over the years.
DPV
Diver Propulsion Vehicle: If you’re just cruising along a reef, your legs are usually enough, but if you need to travel greater distances between points, if it’s a shipwreck that’s in two places or you’re diving one dive-site with a gap between, an electric motor attached to a propeller is a nice addition, especially if you’re fighting current. A DPV can be quite handy.
DV
DV is your Demand Valve and most commonly refers to your second stage. It’s not so commonly used any more, but if someone refers to their DV, they’re probably talking about their second stage.
PP
Partial Pressure: When you get into mixed-gas diving, nitrox and whatnot, you’ll learn about partial pressures. If you break up the composition of the gas you’re breathing into fractions and multiply by the ambient pressure, it helps us work out when it’s safe or dangerous to breathe a gas mix. If the partial pressure of something like oxygen is too high, it becomes dangerous.
RIB
RIB is sometimes spelled RHIB, which stands for Rigid Hulled Inflatable Boat, but the ‘hulled’ can usually be taken as read. The bottom of the boat, or the keel, is made from a hard solid material – a rigid hull – with inflatable tenders around the side.
SAC
Surface Air Consumption Rate or, simply, how much gas you breathe in pressure units like bar or PSI per minute as if you were on the surface. By keeping track of your SAC rate, you can aim to improve your bottom time and plan your dives better. Your SAC rate is cylinder-size specific, so if you swap cylinders you will need to recalculate your SAC.
RMV
Similar to SAC, RMV is your Respiratory Minute Volume. It’s measured in litres per minute, which can be more useful than pressure units. If you know how many litres of gas you breathe in a minute on the surface and the amount of gas in the cylinder, you can work out how long you can breathe from that cylinder at a given depth.
LDS
Local Dive Shop or Local Dive Centre. It’s the dive centre closest to where you’re based, where you tend to get your air-fills, spare parts and dive training. They’re in a tough position right now within the industry, and we need to support our local dive stores to keep them in business.
HP + IP
High Pressure and Intermediate Pressure. Sometimes it’s HP and LP, which stands for low pressure. These acronyms normally refer to your regulator first stage, either the ports on the first stage or the hoses that come out of them. HP is the high-pressure side that deals with the full pressure of your cylinder. IP is the lower-pressure side that feeds your second stages and low-pressure inflator hoses.
STA
Single Tank Adapter: This is more for backplate and wing BCDs. For a more stable set-up, you can fit a U-shaped cradle to the back of your backplate and wing to stop your cylinder from rolling around on your back. There is no secure way of bolting them on but. with a single tank adapter, it’s a physical cradle that stops them from twisting and rolling.
MSW + FSW
Metres of Sea Water or Feet of Sea Water. The salinity of salt water affects the pressure at depth and can throw your dive-computer off by a few per cent. Most dive-computers have a setting for salt or fresh water for accuracy.
FFM
FFM is a Full Face Mask for either scuba diving or snorkelling. Instead of a classic half-mask and separate mouthpiece, you can combine them for something that covers your whole face, allowing you to talk, breathe through your nose and keep your face out of cold water.
GF
GF is your Gradient Factor. When you get more into your diving, you can adjust some of the algorithms in your computer to tailor how conservative or aggressive they are about decompression. You’ll have a GF high and a GF low. They adjust how long your stops are in the water and at which depth they start.
OPV
Over Pressure Valve or Over Pressure Relief Valve. This is like a fusebox that will blow if the current gets too high. If the pressure in a certain area increases to where it could cause damage, an over pressure valve vents any excess pressure. You have them on BCDs, DSMBs, and some first stages on regulators.
WOB
Work Of Breathing: You’ll probably find this in a regulator manual or description online. It’s how hard you have to suck or blow to open each valve on a second stage. Ideally, you want the lowest work of breathing possible so that your body isn’t working hard to move gas in and out of your lungs.
OOA
Out Of Air: You should have practised this a few times in your foundational course. It’s when one or more divers has run out of air or any gas to breathe, for whatever reason.
FFA
Feet First Ascent, this is found most commonly in new drysuit divers. If the air-pocket in your drysuit goes to your feet, that will be the floatiest part, leading to a runaway ascent feet first. You are trained in how to prevent this during the drysuit course.
PDC
Personal Dive Computer, or the computer you use to monitor your diving and stay safe in the water. If you’re using someone else’s, it’s not your PDC. Typically, that’s the one you own and strap to your wrist or console.
AI
Air Integrated. In the scuba world, it means that your dive-computer has a wireless air transmitter that fits to your regulator and tells your dive-computer how much gas you have left in the tank. You don’t have to look at your gauges; it’s all on your computer. It also works out lots of clever things based on your breathing rate.
RGBM
Reduced Gradient Bubble Model. This is one of the algorithms that some dive-computers use to work out how much nitrogen is in your tissues and other factors. There are a handful of algorithms, but RGBM is one of the best known.
Now, I’m sure there are plenty more scuba-diving acronyms the diving community has come up with, especially when your diving starts getting more technical. If you know of others, pop them down in the comments below. There are plenty of funny ones as well.
Remember to check out scuba.com if you need new dive gear and visit the Scuba Diving website if you’re interested in a magazine subscription.
