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Can Mouthpiece Retaining Straps Improve Rebreather Diving Safety?

In this issue of InDepth, we explore the value and efficacy of using mouthpiece retaining straps aka ‘gag straps’ to improve rebreather diving safety. Though few tech divers use them today, a good case can be made for their use as evidenced by this reasoned case made by DAN’s Reilly Fogarty.



By Reilly Fogarty
Header photo by
Reilly Fogarty

Be sure to check out the following stories:

InDepth: RTC Launches New Rebreather Safety Initiative

InDepth: Increasing The Probability Of Surviving Loss Of Consciousness Underwater When Using A Rebreather by Paul Haynes

InDepth: A Mouthpiece Restraining Strap Just Might Save Your Life by Andrew Fock

InDepth: Where do Agencies and Manufactures Stand on Mouthpiece Restraining Straps?

We surveyed CCR divers from around the world. Here are the results.

Rebreathers are excellent tools for extending dives and pushing the limits of human exploration. Unfortunately, discussing how best to set up your rebreather in any public forum can push the limits of human patience. The cost, the training, and the experience required to dive a rebreather can lead to strong opinions, and the debates about the commercially available options are endless. In these debates, consideration of important safety features can be lost. 

Among these features are mouthpiece retainers sometimes referred to as “gag straps.”.The concept is neither new nor revolutionary—most are simple rubber straps designed to hold the circuit in a diver’s mouth in case of loss of consciousness. Some designs feature a half or a full face mask. The purpose of the feature is to keep water out of the airway of a diver who has lost consciousness. Beyond a few configuration options, there are few differences between most of the units available to recreational divers. 

Research has shown that mouthpiece retainers offer a real benefit in terms of safety, so regardless of how you choose to configure your rebreather, a loop-retaining device is crucial. 


Retainer strap connected to the mouthpiece.
Photo by AP Diving.

Understanding what kills rebreather divers is complicated by the small number of participants and the problem of separating anecdotes from statistically relevant data in small incident sample sizes. Estimates of the total number of rebreather divers globally range from 6,000–20,000 divers; neither manufacturers nor training agencies provide their sales or certification numbers to the public. A safe estimate of active rebreather divers is generally considered to be around 14,000. 

The military and to a lesser extent the commercial diving community (commercial Saturation divers use rebreathers for bailout) represent other groups of users. Both of these communities use slightly different equipment and adhere to much stricter operational protocols. Military/commercial use and fatality numbers are largely unknown to the public  as well, but there are some exceptions that have proven enlightening. Based on incident reports, DAN Annual Diving Report analysis, and a series of DAN Rebreather Forum meetings, the single largest killer of rebreather divers is drowning.

Based on incident reports, DAN Annual Diving Report analysis, and a series of DAN Rebreather Forum meetings, the single largest killer of rebreather divers is drowning. 

While this may sound unsurprising or even obvious, it illustrates that what kills rebreather divers is not freak accidents or the increasing number of health issues we see in the larger general population of recreational divers. This shows that rebreather fatalities can largely be attributed to some kind of drowning—generally subsequent to loss of consciousness via hypoxia, hyperoxia or hypercapnia. It’s in addressing this cause of mortality among rebreather divers that diver supply valve (DSV) retainers come into play. These devices aren’t a catch-all designed to save divers from their own mistakes or drown-proof undertrained, would-be explorers. What they do is to provide a measure of safety in loss-of-consciousness events and to measurably decrease fatalities. 

Equipment Options

Photo courtesy of rEVO.

These mouthpiece retainers come primarily in two variations. The first is a retainer strap, like a mask strap, that attaches to a rebreather mouthpiece and is positioned behind the head. This strap attaches to a device that will seal around the lips (such as the lip seal on a Drager Safety Strap). The second option is a full face mask designed for CCR use, like the Draeger Panorama, or a partial mask design like the Kirby Morgan M48. There are now several commercially available options for rebreather divers looking for full or partial mask options; as long as the device is intended for rebreather divers and adequately minimizes dead space, it can  reasonably be considered for use. Excessive dead space in a full face mask can lead to unintended CO2 retention, which poses a greater hazard to rebreather divers than it does to open-circuit divers. 

Both options function similarly, sealing the rebreather circuit to the lips and allowing the diver to continue breathing. It’s important to note that losing control of the circuit while underwater will also result in the loss of loop volume and a commensurate decrease in buoyancy, exacerbating any issues that led to the initial loss of control. This type of compounding incident is common among new rebreather divers and difficult to recover from. 


Given the size of the market and the limited availability of military research, it’s not surprising that statistical studies of mouthpiece retainers are difficult to find. While it’s true that case studies abound, and many provide valuable information, the compounding nature of rebreather accidents makes it difficult to determine a single incident catalyst rather than guess at the most likely contributing factors to a fatality. What we know about mouthpiece retainers comes primarily from two studies. The first reviews 54 loss-of-consciousness events in military rebreather diving (Haynes, 2016), while the second reviews 153 diving injuries among French military rebreather divers (Gempp, 2011). 

The Haynes paper begins by reviewing the range of issues created by the initial adoption of rebreathers by recreational divers. The early modifications, protocol creations, and fatalities illustrated incident statistics surprisingly close to what we see now, with “inappropriate gas” causing more than half of all rebreather fatalities in Haynes’ data analysis. This category (in this analysis) indicated a rebreather-delivered gas causing hypoxia, hypercapnia, or hyperoxia rather than a tank of mislabeled open-circuit gas. This holds true with what we now know about rebreather fatalities and serves as the motivation for Haynes’ review of mouthpiece retainers to minimize the fatalities caused by the resulting loss of consciousness in these incidents. While the Haynes paper goes on to cite military adaptations of mouthpiece retainers, case reviews, and expert testimonial, the most educational data cited is taken from the Gempp paper. 

Photo courtesy of Divesoft.

Descriptive Epidemiology of 153 Diving Injuries with Rebreathers Among French Military Divers from 1979 to 2009 confirms both the Haynes and industry data, with gas toxicity causing 68% of injuries. More importantly for our purposes, it reviews 104 cases of gas toxicity with 54 of those resulting in impairment or loss of consciousness in the water. Of these, the outcome was “always favorable” if the diver could be retrieved to the surface. Among the loss-of-consciousness events, only 3 fatalities were recorded. The paper goes on to state that “gas toxicities are frequently encountered by French military divers using rebreathers” but that the low fatality rate can be attributed to strict safety protocols, specifically the “mouthpiece strap, buddy team with link, and diving instructor with open circuit to lend assistance if necessary during training” (Gempp, 2011).  

Both papers are clear about the use of mouthpiece retainers saving lives among the population studied. As with any research, it’s important to note that this may not apply directly to your diving. It’s true that mouthpiece retainers showed very promising results in case studies as well as incident reviews, but the subjects do not represent most recreational divers. Not only do both studies focus on military divers in better physical condition and with better equipment maintenance, but their subjects adhere more strictly to safety protocols and receive significantly more training than recreational divers. 

The lack of training in particular is what brings issues like bail-out protocols to light. It’s true that bailing out with either a mouthpiece retainer or full face mask becomes somewhat more complicated, and the addition of a bailout-valve adds additional opportunities for user error. With adequate training and emergency protocols it seems unlikely that any of these concerns would notably increase risk, but that’s not something we have the data to confirm just yet. 

For now, consider the research, and consider how you dive: do you have enough experience and training to add a mouthpiece retainer to your configuration? If the data applies to your diving, a mouthpiece retainer might just save your life. 


Haynes, P. (2016, December). Increasing the probability of surviving loss of consciousness underwater when using a rebreather

Gempp, E. (2011). Descriptive Epidemiology of 153 Diving Injuries with Rebreathers Among French Military Divers from 1979 to 2009.

Dive Deeper:

Mouthpiece Retaining Straps: Discussion on CCR Explorers
A Survival Guide for Rebreather Diving, by Paul Haynes

When he’s not working with DAN on safety programs, Reilly Fogarty can be found running technical charters and teaching rebreather diving in Gloucester, Mass. Reilly is a USCG licensed captain whose professional background includes surgical and wilderness emergency medicine as well as dive shop management.

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InDEPTH’s Holiday Rebreather Guide 2023

Making a list. Checking it twice. Gonna find out which breathers are naughty or nice. That’s right! It’s time again for InDEPTH’s Holiday Rebreather Guide. This year, we are featuring 32 models of back, sidemount and chest mounted rebreathers, including five new units for your shopping enjoyment. So, get out your Pre-Buy Checklist, and that Gift Card (you do have a gift card don’t you?!?), and buy the breather of your dreams. Ho, ho, hose!




by Michael Menduno, Amanda White and Kenzie Potter. Holiday images by Jason Brown, BARDO CREATIVE.

A Guide to Backmount, Sidemount and Frontmount Rebreathers

6 Dec 2023 – Ho ho ho! InDEPTH’s Holiday Rebreather Guide continues to pick up steam (machines). This season we added Mares Horizon semi closed rebreather and Lombardi Undersea Research’s new RD1 back mounted oxygen rebreather. We also added Lungfish Dive Systems “Lungfish,” And iQSub Technologies’ new FX-CCR front mounted breather along with the Flex2 sidemount CCR. As such we believe the Guide is the most complete one on the market! Pst, pst Mr. Scammahorn, are you still there? Happy shopping divers! Ho ho hose!

Remember you can find all of the Rebreather Forum 4 presentations here on REBREATHER FORUM 4

1 Dec 2022 – Ho ho ho! Once again, we have updated InDEPTH’s Holiday Rebreather Guide adding two new rebreathers; the new Gemini sidemount, needle valve mCCR from Fathom Systems, and the Generic Breathing Machine (GBM) front mounted, needle valve mCCR, with a dive computer-compatible, solid state oxygen sensor from Scubatron. We also updated the features on the Divesoft Liberty sidemount, and the JJ-CCR. This year, Vobster Marine Systems was acquired by UK-based NAMMU Tech, which plans to rename and re-issue a version of the VMS Redbare. See link below.

Finally, Innerspace Systems’ founder Leon Scamahorn agreed to work on getting us the needed information to add the storied Megalodon to the Guide. Scratch last year’s coal, Xmas cookies for you Mr. Scamahorn! Happy holidays shoppers, here is our updated rebreather guide! Mind those PO2s!

17 Dec 2021 – Ho Ho Ho! We have updated our Holiday Rebreather Guide with new rebreathers and updated features. Despite repeated requests, the only major closed circuit rebreather we are missing is Innerspace Systems’ Megalodon and its siblings. Tsk, tsk Leon Scamahorn, you’ve been a naughty boy! Behold, here is our updated guide. Mind those PO2s!

Dr. Bill Stone’s manned trial of F.R.E.D. at Wakulla Springs (1987). Photo courtesy of the US Deep Caving Team

However, it took the fledgling tech community at least a decade to adapt mixed gas technology for open circuit scuba, including establishing the necessary supporting infrastructure, which was the first and necessary step in the move to rebreathers. A little more than a decade after Stone showcased FRED, British diving entrepreneur Martin Parker, managing director of then AP Valves, launched the “Buddy Inspiration,” the first production closed circuit rebreather designed specifically for sport divers, earning him the moniker, the “Henry Ford of Rebreathers.” [The brand name later became AP Diving] KISS Rebreathers followed a little more than a year later with its mechanical, closed circuit unit, now dubbed the KISS Classic. The rest as they say, is history, our history. 

Buddy Inspiration advertisement from 1998. Courtesy of AP Diving.

Today, though open-circuit mixed gas diving is still an important platform, rebreathers have become the tool of choice for deep, and long exploration dives. For good reason, with a greatly extended gas supply, near optimal decompression, thermal and weight advantages, bubble-free silence, and let’s not forget the cool factor, rebreathers enable tech divers to greatly extend their underwater envelope beyond the reach of open circuit technology. 

As a result, divers now have an abundance of rebreather brands to choose from. Accordingly, we thought it fitting this holiday season to offer up this geeky guide for rebreather shoppers. Want to find out whose breathers are naughty or nice? Here is your chance.

Your Geeky Holiday Guide

The idea for this holiday guide was originally proposed to us by Divesoft’s U.S. General Manager Matěj Fischer. Thank you Matěj! Interestingly, it doesn’t appear to have been done before. Our goal was to include all major brands of closed circuit rebreathers in back mount and sidemount configuration in order to enable shoppers to make a detailed comparison. In that we have largely succeeded. We also included Halcyon Dive Systems’ semi-closed RB80 and more recent RBK sidemount unit, which are both being used successfully as exploration tools. 

Absent are US-based Innerspace Systems, which makes the Megalodon and other models, as well as Submatix, based in Germany, which manufactures the Quantum and sidemount SMS 200, neither of which returned our communications. M3S, which makes the Titan, declined our invitation to participate, as they recently discontinued their TITAN CCR—they will be coming out with a replacement unit, the TITAN Phoenix CCR in the near future. We did not include the MARES Horizon, a semi-closed circuit rebreather that is aimed at recreational divers. No doubt, there may be brands we inadvertently missed. Our apologies. Contact us. We can update.

Update (22 Jul 2021) – French rebreather manufacturer M3S contacted us and sent us the specs for their updated chest-mounted Triton CCR, which are now included in the guide.

Update (9 Dec 2020) – Submatix contacted us and the Guide now contains their Quantum (back mount) and SMS 200 (sidemount) rebreathers. We were also contacted by Open Safety Equipment Ltd. and have added their Apocalypse back mounted mechanical closed circuit rebreather. We will add other units as they are presented to us by the vendors. 

It’s The Concept, Stupid

The plan was to focus on the feature sets of the various rebreathers to provide an objective means to compare various units. But features by themselves do not a rebreather make. As Pieter Decoene, Operations Manager at rEvo Rebreathers, pointed out to me early on, every rebreather is based on “a concept,” that is more than just the sum of its features. That is to say that the inventors focused on specific problems or issues they deemed important in their designs; think rEvo’s dual scrubbers, Divesoft’s redundant electronics, or integration of open and closed circuit in the case of Dive Rite’s recently launched O2ptima Chest Mount. Shoppers, please consider that as you peruse the various offerings. My thanks to Pieter, who helped us identify and define key features and metrics that should be considered.

  • Area 9

Though not every unit on the market has been third-party tested according to Conformitè Europëenne (CE) used for goods sold in the European Union, we decided to use CE test results for some of the common feature benchmarks such as the Work of Breathing (WOB), and scrubber duration. For vendors that do not have CE testing, we suggested that they use the figures that they publicize in their marketing materials and asked that they specify the source of the data if possible. As such, the guide serves as an imperfect comparison, but a comparison nonetheless.

Santa’s Little Helper: Meet Rufus, BARDO’s Chief Muse Officer (CMO)

Also, don’t be misled by single figures, like work of breathing or scrubber duration as they serve only as a kind of benchmark—there is typically a lot more behind them. For example, whether a rebreather is easy to breathe or not is a function of elastance, work of breathing (WOB) and hydrostatic imbalance. In order to pass CE, the unit must meet CE test requirements for all three issues in all positions from head down, to horizontal trim, to being in vertical position (Watch that trim!), to lying on your back looking upwards. It’s more difficult to pass the tests in some positions versus others, and some units do better in some positions than others. 

The result is that some of the feature data, like WOB, is more nuanced than it appears at first glance. “The problem you have is people take one value (work of breathing for instance) and then buy the product based on that, but it just isn’t that simple an issue,” Martin Parker explained to me. “It’s like people buying a BCD based on the buoyancy; bigger is better, right? Wrong! It’s the ability of the BCD to hold air near your centre of gravity determines how the BC performs. With rebreathers you can have good work of breathing on a breathing machine only to find it completely ruined by it’s hydrostatic imbalance or elastance.”

Due to their design, sidemount rebreathers are generally not able to pass CE requirements in all positions. Consequently, almost all currently do not have CE certification; the T-Reb has a CE certification with exceptions. However, that does not necessarily mean that the units haven’t been third-party tested. 

Note that the guide, which is organized alphabetically by manufacturer, contains the deets for each of their featured models. In addition, there are two master downloadable spreadsheets, one for back mounted units and one for sidemount. Lastly, I’d also like to give a shout out to British photog phenom Jason Brown and the BARDOCreative Team (Thank you Georgina!), for helping us inject a bit of the Xmas cheer into this geeky tech tome [For insiders: this was Rufus and Rey’s modeling debut!]. Ho, ho, hose!

With this background and requisite caveats, we are pleased to offer you our Rebreather Holiday Shoppers’ Guide. Happy Holidays!!

Note – Most prices shown below were specified by manufacturer before tax.

Backmount Rebreathers

* In 2005, AP Diving launched its Vision electronics with In-Plane Switching (IPS) which enhances colour and visibility
**Typical scrubber duration using AP Tempstik increases practical duration to more than double CE test rate figures – as the AP Tempstik shows scrubber life based on actual work rate, water temperature and depth.
*** The work of breathing is the effort required to push gas around the breathing circuit BUT that figure alone is meaningless without knowing two other parameters: Hydrostatic load and elastance. Note that AP Diving rebreathers meet the CE requirements in all diver attitudes for both Hydrostatic Imbalance 0 degrees (horizontal, face down) and Hydrostatic Imbalance +90 degrees (vertical, head up.)
**** APD’s handset offers a “dual display” feature showing data from both controllers on the same handset. The user can also see the gradient factors chosen and the mVolt outputs of the cells by holding a button down.
* Divesoft will offer an upgrade for existing Liberty users
* Note that we plan to re-release our “Intervention CCR” (iCCR) in 2021. The unit was withheld due risk of loop being force dived when unsafe (pending re-release 2021).This enables the diver the option to manually trigger bailout to a known safe OC gas at any time with one finger and/or auto-bailout the diver if loop gas being breathed reaches unsafe level. Either Hi/Lo PPO2 or high End-Tidal CO2.
**For CE certification the recommended Apocalypse Type IV CCR scrubber duration is 2hr 45min to a maximum dive profile surface to surface of 100m in 4’C water to 2.0% SEV (20mb) at the mouth.
***iCCR (2009) 3x digital galvanic coax, iCCR (2021) x2 galvanic 1x solid state
****All performance data near near identical to single scrubber option other than increased scrubber duration of up to 5 hrs to 100 m profile in 4’C water)
Published Testing: .pdf
* CisLunar series, MKVI 2009, SE7EN 2013, SE7EN+ 2019
** 40 m coldwater EN14143
*** Backmounted Trimix 10/70, 40M test: Backmounted Air
**** SE7EN+ Sport EU incl (harness, wing, computer, cylinders and sensors)
  • Halcyon Sidemount

Note – Vobster Marine Systems were acquired by UK-based NAMMU Tech, which plans to rename and re-issue a version of the VMS Redbare (formerly the Sentinel) at some point in the future. See: Atlas CCR


Rey says he’s sticking to open circuit. What’s a Santa to do?

Sidemount Rebreathers

*Pre 2021 units are upgradebale
* For a tour of KISS rebreathers see:

Frontmount Rebreathers

*Tested with standard DSV, 6l OTS counterlungs, Upright/face forward, 40 m depth, 40.0 lpm RMV, Air diluent
**Tested with standard DSV, 45° head up/feet down orientation, 40 m depth, 40.0 lpm RMV, Air diluent
*** Micropore ExtendAir Cartridge:
180 liters of CO2 @ < 50 deg F [<10 C] (130 minutes @1.35lpm CO2)
240 liters of CO2 @ 50-70 deg F [10-20C] (180 minutes @ 1.35lpm CO2)
300 liters of CO2 @ >70 deg F [>20C] (220 minutes @ 1.35lpm CO2)
Test Parameters: 40 lpm RMV 1.35 lpm CO2130 fsw (40 m) depth Granular duration may be similar, but can vary greatly depending upon the type of granular and packing technique

 Download our two master spreadsheets, one for back mounted units and one for sidemount to compare rebreathers.

Special thanks to Amy LaSalle at GUE HQ for her help assembling the feature spreadsheets.

Michael Menduno is InDepth’s editor-in-chief and an award-winning reporter and technologist who has written about diving and diving technology for 30 years. He coined the term “technical diving.” His magazine aquaCORPS: The Journal for Technical Diving (1990-1996), helped usher tech diving into mainstream sports diving. He also produced the first Tek, EUROTek, and ASIATek conferences, and organized Rebreather Forums 1.0 and 2.0. Michael received the OZTEKMedia Excellence Award in 2011, the EUROTek Lifetime Achievement Award in 2012, and the TEKDive USA Media Award in 2018. In addition to his responsibilities at InDepth, Menduno is a contributing editor for DAN Europe’s Alert Diver magazine and X-Ray Magazine, a staff writer for, and is on the board of the Historical Diving Society (USA)

Amanda White is the managing editor for InDepth. Her main passion in life is protecting the environment. Whether that means working to minimize her own footprint or working on a broader scale to protect wildlife, the oceans, and other bodies of water. She received her GUE Recreational Level 1 certificate in November 2016 and is ecstatic to begin her scuba diving journey. Amanda was a volunteer for Project Baseline for over a year as the communications lead during Baseline Explorer missions. Now she manages communication between Project Baseline and the public and works as the content and marketing manager for GUE. Amanda holds a Bachelor’s degree in Journalism, with an emphasis in Strategic Communications from the University of Nevada, Reno.

Kenzie Potter Stephens is a production artist for InDepth as well as part of the GUE marketing team. She earned her BS degree in Industrial Engineering and Marketing at the Karlsruhe Institute of Technology (KIT) in Germany, which assists her in using her multicultural upbringing to foster international growth within the community. In addition to her activities as a yoga teacher and an underwater rugby trainer, she has completed her GUE Tech 1 and Cave 1 training and is on her way to becoming a GUE instructor. Not letting any grass grow under her feet, she has also taken on a second major in biochemistry in order to create a deeper understanding of our planet’s unique ecosystems as well as the effect of diving on human physiology.

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