Understanding Rebreather Diver Lingo

Hollis Prism 2 Rebreather Diver

Users guide to understanding those confusing acronyms commonly used by Rebreather Divers

I’ve never considered myself to be a “tech diver.” But in many cases, I will use the equipment, training and protocols of technical diving in order to gain access to caves, deep wrecks or skittish animals. My dive locker contains one special piece of equipment that would instantly brand me as a “techie” in most diving circles: a closed-circuit rebreather. But ironically, the vast majority of dives I’ve logged on this type of equipment have, and likely will continue to take place well within the depth limits of recreational diving.

I always get a kick out of how technical divers love to use all sorts of acronyms to describe everything from physics, and equipment to diving procedures and methodology. But when it comes to whom in the technical diving community with the most confusing number of acronyms, the rebreather divers are in a class by themselves. They seem to have a language all to their own, and it can be difficult to decipher.

Here’s an example of what you might see on a technical diving forum like RebreatherWorld.com or CCRExplorers.com

Most RB’s are sold with a standard DSV mouthpiece where as CCR models like the KISS come with a BOV as part of the loop to serve as a OCB, which can be fitted to FFM. Now the point of a BOV or OC/DSV is for the diver to switch to OC mode from CC mode should their RMV and SAC rate go through the roof from elevated CO2, which is where WOB comes into play.

In addition to this add on, some RB divers, largely eCCR and mCCR users, like to have a HUD or HUS (like a NERD) mounted on their DSV or BOV to better monitor their PPO2 during long RT’s particularly when a DPV is used.

Still with me?

If not, you can decipher the alphabet soup by referring to the following list of acronyms most commonly used by rebreather divers:

ADV – Automatic Dilutant Valve – adds Dil to the rebreather’s breathing loop during decent..

APD – Absolute Pressure Diving – in addition to the term, also refers to company that manufactures the Inspiration and Evolution Rebreather, which are sometimes referred to by non fans of the rebreather as a YBOD.

aSCR – Active addition type semi-closed rebreather.

BMC – Back Mounted Counter Lungs.

BOB – Bail Out (re-)Breather

BOV – Bail Out Valve, shorter way of referring to an open circuit second stage regulator built into a rebreather mouth piece.

CC – Closed Circuit

CCBA – Closed Circuit Breathing Apparatus.

CCR – Closed Circuit Rebreather

CL – Counter Lung.

Dil – Short for Dilutant, the gas typically with no more than 21 % O2 used to dilute the O2 content inside the rebreather’s breathing loop.

DPV – Diver Propulsion Vehicle. Most non technical divers call them scooters.

DSV – Dive Surface Valve, the mouthpiece in a rebreather loop that can be open and closed by the rebreather diver.

DV – Demand Valve.

eCCR – Electronically controlled CCR or CCBA

FFM – Full Face Mask.

FFW – Feet of Fresh Water.

FSW – Feet of Seawater.

GEM – Gas Extension Mechanism. In short, a Semi-closed Rebreather (SCR).

GF – Gradient Factor – When it comes delving into decompression theory, be prepared to go down the rabbit hole on this subject.

GUE – Global Underwater Explorers – seen it also represent Generally Unresponsive to Electronic CCR’s and dive computers.

hCCR – h stands for hybrid where the CCR features both mechanical and electronic systems to run the unit.

HH – HammerHead – Specific brand of CCR named after the Hammer Head electronics made by Juergensen Marine.

HPNS – High Pressure Nervous Syndrome

HUD – Heads Up Display – part of a rebreather’s system to display very basic PPO2 levels with colored LED lights.

HUS – Heads Up Screen – another type of HUD system but with a LED screen providing specific information.

ISC – Innerspace Systems Corporation – manufacturer of the Megalodon CCR.

KISS – Keep It Simple Stupid – this is also the name of a rebreather manufacturer of both mCCR’s and pSCR’s. Don’t know what those last are? Keep going.

MAV – Manual Add Valve – a devise featured in both mCCR’s and hCCR’s.

mCCR – Mechanical (or Manual) Closed Circuit Rebreather – type of CCR that is not reliant on electronics, usually features a MAV.

MDT – Maximum Dive Time.

MFW – Meters of Fresh Water.

MGR – Mixed Gas Rebreather – one that is using a gas mixture other than air in the Dil.

MUPPET – Most Uncoordinated or Useless Person PADI Ever Trained. I know its mean, but I can’t take credit for it either.

MSW – Meters of Seawater.

NERD – Near Eye Reading Display – another type of HUD or HUS manufactured by Shearwater Research that features complete PPO2 and dive profile information.

OC – Open Circuit, used when referring to being on scuba or blowing bubbles underwater.

OCB – Open Circuit Bailout – you guessed it, another way of saying BOV.

OC/DSV – Open Circuit integrated second stage in a Dive Surface Valve. In short a BOV

OPV – Overpressure Relief Valve – featured found in most rebreather loops to all excess gas to vent to prevent over expansion.

OTS – Over the Shoulder Counter Lungs.

OTT – Oxygen Tolerance Test.

OTU – Oxygen Toxicity Unit.

O2 – Oxygen.

PPO2 – Partial Pressure of Oxygen – very important to all rebreather divers.

pSCR – Passive Addition type SCR.

Keep going, you’re not done yet!

PVR-BASC – Passive Variable Respiratory-minute-volume Biased Addition Semi-Closed Rebreather. In short, a fancy way of addressing a mechanical pSCR.

P2 – Prism II – eCCR manufactured by Hollis.

RB – Rebreather – used by forum posters too lazy to spell rebreather.

RMV – Respiratory Minute Volume

RT – Run Time – the total time a rebreather diver spends underwater during a dive.

SAC Rate – Surface Air Consumption Rate.

SCBA – Semi-Closed Breathing Apparatus.

SCR – Semi Closed Rebreather.

SFW – Sure, Fine, Whatever.

SMB – Surface Marker Buoy.

SPG – Submersible Pressure Gauge.

STROKE – Society of Technical Risk-Optimizing Karst Explorers – applied to cave divers who are not GUE.

TOS – Top of the Shoulder Counter Lungs.

UBA – Underwater Breathing Apparatus.

VENTID – Vision, Ears, Nausea, Twitching, Irritation, Dizziness – signs, symptoms of oxygen toxicity to look for.

WOB – Work of Breathing – this is subject every rebreather diver will talk about, sometimes endlessly, when discussing the breathing merits (good or bad) of a particular rebreather, DSV or BOV. Often RMV and SAC Rates are included in the same sentence.

YBOD – Yellow Box of Debt. Yellow Box of Debt. Often used to denote the Inspiration or Evolution Rebreather manufactured by AP due to their pricy nature like most closed circuit rebreathers. Yes, this is not a cheep sport to be in.