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Where Do Training Agencies and Manufacturers Stand on Mouthpiece Straps?

We asked a variety of tech agencies and CCR manufacturers where they stand on mouthpiece retaining straps and whether or not they advocate their use and or mention them in courses.

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Header photo by Jesper Kjoller

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

Can Mouthpiece Straps Improve Safety?

A Mouthpiece Restraining Strap Just Might Save Your Life

Why GUE Has Not Adopted The Strap

First and foremost, GUE constantly evaluates and develops technologies and methodologies with the ultimate goal of offering increased safety, efficiency, and enjoyment to our divers. One such device is the Mouthpiece Retaining Strap (MRS) or more commonly called—the gag strap. The purpose of the MRS is to secure the diver’s mouthpiece (DVS or BOV) in place using an adjustable rubber band around the diver’s head. In theory, this would retain the mouthpiece in the diver’s mouth even during an adverse event leading to unconsciousness and thereby prevent drowning and death. 

The origin of the MRS comes from the military diving community where it is used as an alternative to Full Face Masks (FFM). There is at least one study indicating a reduced risk of drowning while diving rebreathers under military operations with the use of a MRS. However, one should keep in mind that military rebreather diving applications are quite different compared to our technical diving application. Where the military divers carry no bailout, we certainly do. We also have more obvious and less concealed communication and information devices, such as bright head Up Displays (HUD) and controllers giving us a fair chance of detecting malfunctions. 

Since our technical diving application is different, and our methods for bailout need to be uncomplicated and unrestricted, we have found that the use of the MRS would be unlikely to reduce the risks, and as such, we don’t advocate for the use. We don’t prevent the use per se, but we prefer a holistic and consistent approach when feasible. 

-Richard Lundgren, GUE Technical Administrator

Reference:

Haynes P. Increasing the probability of surviving loss of consciousness underwater when using a rebreather. Diving Hyperb Med.2016 Dec;46(4):253-259.

Photo by Ortwin Khan.

PADI’s Position on Retaining Straps

Community practice regarding the use of retaining straps in CCR diving remains divided, so at present, the choice to use them or not lies with the instructors and their students. The only exceptions are if the particular CCR manufacturer prohibits or requires strap use with their units, in which case manufacturer requirements should be followed. If and as community practices change, the requirements in PADI courses will change accordingly.

Karl Shreeves, Technical development executive, PADI

RAID Encourages Their Use

RAID encourages the use of a retaining strap, but it is not mandated. Simple logic dictates that some CCR users do not have a true BOV installed and do not have off-board diluent (bailout gas) plugged into the unit. A retaining strap/gag-strap may not be the best option in that case. (Personal note: When diving my old pelagian rebreather, I have the mouthpiece  “loose” and a bailout second stage on a necklace. I only had to use it in earnest once but I believe it would have been a slower switch from the loop to OC if I’d worn the strap.)

That said, the unit I dive most of the time has a BOV (good idea) and I always wear a retainer. I am thankful for it on EVERY long dive because it does an amazing job of helping to alleviate jaw fatigue. An added benefit is that it does prevent the mouthpiece dropping out of a diver’s mouth whenever they are gobsmacked by the behaviour of others. 

Steve Lewis, RAID training director

Photo courtesy of rEVO.

ANDI Says Usage is Optional

We have decided to add mouthpiece retaining straps to all of our CCR texts along with a few photos and explanations, in the same way that we explain the Full Face Mask. The benefits are these…The deficits are these…

This will show the students the safety advantages, how to use the device and when it would be used. Usage is optional. A limitation caused by the usage of a strap is increased difficulty and additional steps in performing off-board gas switches. Instructors agree that its use adds to potential issues during training.  

Eduardo Jaimes Fabres, our training director commented that “During the last DEMA show I saw a good option made by AP Diving.” It’s basically a silicone strap with two soft large O-rings. It looks good, inexpensive and the user can still use his/her mouthpiece. My personal preference is a standard DSV or BOV with quick access to bail-outs. In the ANDI system a user can dive safely with the DSV and a redundant breathing system (RBS), which ANDI advocates for all divers and levels. 

The primary reason for use of the mouthpiece retainer strap is its protection from drowning during a CNS seizure. That’s it. If one is running the bottom mix at a PO2 of 1.2-1.3 it seems to be a quite unnecessary precaution.  Perhaps a better question for the industry; “Is there any evidence of CNS oxygen toxicity at 1.5, 1.45. 1.4?”

Sorry for the history lesson here but I remember discussions alluding to the dangers of a PO2 dosage of 1.6 atm for open-circuit SafeAir (nitrox) diving, even though no proven incidents were documented at that dosage. Then we stated that 1.5 is safer. Oxygen management is very difficult and unpredictable. 1.4 is even safer still.  Well… for longer dives we should be using 1.3.  Extended range diving is best served with 1.25 oxygen dosages.  Keep going at this and we are back to diving air with fancy gas controllers. 

Edward A. Betts, founder and Executive Director, ANDI International 

Photo courtesy of AP diving.

TDI|SDI|ERDI|PFI 

Did not wish to take a position at this time.

Rebreather Manufacturers

AP Diving Is Favorable And Supplies A Strap

On balance, we are in favour of mouthpiece straps. On longer dives they can reduce jaw fatigue, but this can also be done by ensuring the mouthpiece hose lengths are correct for you—too many divers look like they’re wearing a set of bagpipes when they dive. 

Of course, straps are like a seatbelt in a car from a safety point of view, they’re there to help if you have an accident. Prevention of accidents is of course the first priority, but it is clear a lot of things have to line up for a mouthpiece strap to be of any use in an emergency situation; the mouthpiece strap would only be of use if a dive buddy is present AND is capable of offering assistance, AND if the diver does still manage to make a seal at the mouthpiece despite being unconscious. So you can see a lot of things need to be in line for the strap to be of any use in an emergency, and for that reason, many divers don’t see the benefit in one. We do mention the benefits of the strap in the instruction manual and do offer a strap as an optional extra.

Martin Parker, Managing Director AP Diving

Photo courtesy of Divesoft.

Divesoft Encourages and Supplies A Simple Strap 

We supply our Liberty rebreathers with an elastic bungee cord, which serves as a simple retaining strap. But it is just a simple solution. We also offer the gag strap as an option in our configurator. Unfortunately, we do not currently mention retainer straps in our user manual, but it is a good idea to add it to the manual and also mention it in official factory training powerpoint slides as well.

We definitely advocate their use. I was a part of a team which researched the probability of rescuing an unconscious rebreather diver. The result of the study was absolutely clear. A diver with the gag strap has a much higher chance to survive going unconscious, and a very low chance without it. I really appreciate InDepth’s effort to address this, because I think this is a very important but unfortunately neglected topic.

-Jakub Šimánek, Factory Instructor Trainer Divesoft

Photo courtesy of rEVO.

rEVO Has Supplied and Advocated from Day One

Since the start of the rEvo production, we have always been (and we were the first for civilian use) supplying mouthpieces with lip seal and retainer straps standard on all units. It’s the same for training on rEvo units: the use of this mouthpiece with straps has always been mandatory, and it is mentioned in the user manual and in all training material. 

Why? Simple! Because underwater, people never die because of bad gas (almost never…). If they die, they do because they breathe water. So if you can prevent, or delay, the breathing of water, you increase the likelihood of survival. Furthermore, a correctly fitted gag strap prevents buoyancy loss in case of unconsciousness .

Paul Raymaekers, rEvo Rebreathers founder & CEO

Hollis Offers A Strap for the European Market & When Requested

With the recent CE approval of the Prism 2, we are offering a mouthpiece retention strap for the European market purchases and for anyone that requests one. However, real world use of a strap is very low. Our statement in our user manual is as follows, “A mouthpiece retaining strap is included with the Prism 2 Rebreather. This part minimizes the ingress of water during normal use and ensures the mouthpiece is held in place and the diver remains on the loop in the event of a diver falling unconscious or having a convulsion while underwater.”  

Nick Hollis, Brand Manager, Oceanic & Hollis

Dive Rite Says Watch Your PO2s

We have looked at the issue, but the only one I know of is the Drager strap. I have tried variations, but I just don’t like it and we don’t provide one.  It can only help in the case of O2 toxicity? Survive the seizure? With regard to CO2 build-up or hypoxia, I’m not sure what the results would be. At the end of the day, should we react to divers not watching their PO2 or maintaining gear, by forcing everyone to use what I see as an uncomfortable strap because it has saved a few lives? Or could the incident have been avoided in the first place? 

Lamar Hires, Founder and president Dive Rite

Inner Space Says Good For Jaw Fatigue 

My experience with a head straps began in the military with Draeger LAR V (oxygen) rebreather. Their purpose was not to prevent drowning but to prevent jaw fatigue during the endless hours we spent in the water with a diver surface valve (DSV) in our mouth. You put it on and secured it. Did we always use it? No, and I was a Special Forces Combat Diver, Diving supervisor, and trained with Seal Team Five.

The Combat Diver school did not advocate the strap. I used it but didn’t think it was necessary. It was more in the way with a DSV. I did use a head strap for airborne operations when breathing hoses would flutter during the jump. I also used it with a scooter when hoses can also flutter. However, the LAR V does not have a bailout valve (BOV). I never advocated a strap as a diving supervisor, though I do think you should use one in airborne operations.

As I said, the head strap worked well for preventing jaw fatigue while diving. Also, the metal adjustment clasps on the Draeger strap worked great. I pondered whether to advocate and use a head strap when I started Inner Space. I think it is a good idea if you have a BOV. If you don’t it just slows down your gas switch. Also a lot of BOVs are big and heavy and can easily cause jaw fatigue so it is a good tool for that. In addition, if you passed out, it would aid in your rescue. It is a handy tool.

We looked at alternatives for preventing drowning. An old school half-facemask will prevent wet drowning. I have a good one from the fifties that seals around the mouth and buttons on the side. You still need a mouthpiece with it however to prevent CO2 build up. I think if the community got together it could create a new version of this for tech divers. The advantages are: no jaw fatigue, it seals around the mouth to prevent drowning in case the diver loses consciousness. It could be a little piece of insurance against wet drowning.

Leon Scamahorn, founder and CEO Inner Space Systems

Note that Kirby Morgan Diving System makes half-mask called their M48 MOD-1 and the M48 SUPERMASK.  

Rebreather Forum 3 (2012) Advocated Further Research

Mouthpiece retaining straps were addressed at Rebreather Forum 3, held in Orlando, Florida in 2012 and formed the basis (along with full face masks) of a Consensus Statement by the assembled body. See Rebreather Forum 3 Proceedings (pg 287-302).

Design and Testing 5. The forum identifies as a research question the issue of whether a mouthpiece-retaining strap would provide protection of the airway in an unconscious rebreather diver. 

This is a unique statement as the only one in which we are proposing a research question to the research community. This arose out of Paul Haynes’ advocacy for the use of gag straps. In fact, the resulting discussion made it clear that here was a lot of ambiguity around people’s perceptions. To my knowledge, there are no data or even substantial practical experience that answers that question for us. This statement says, “The forum identifies as a research question the issue of whether a mouthpiece-retaining strap would provide protection of the airway in an unconscious diver.” We need to find a confident ethics committee or an imaginative way of figuring it out. Is there anyone who would like to speak to this?

PAUL RAYMAEKERS: I was not able to follow the presentation. I just hear that the question has no proof or any evidence that a mouthpiece-retaining strap has any efficiency. We did have a fatality a few years ago where it was clearly proven that when the jaw stress completely falls away, a correctly attached gag strap keeps the mouthpiece in place and no water comes into the driver’s lungs.

MITCHELL: If I am interpreting correctly saying there, there has been a case that you know of with a gag strap and mouthpiece [that stayed] in place. John, do you want to speak to this?

CLARKE: I think research would include looking at prior history. One case does not mean this has been solved.

FRANBERG: We come from the military community. I think that if we look at our own data from the fatalities, we may find information on the presence or absence of water in the airway.

MITCHELL: I like that idea. So, what we need is someone who has perhaps a Naval group with keen, young, research-hungry doctors who can start phoning up every navy in the world. My tongue in in my cheek. I have got a smile on my face. I think there probably may be enough information out there already to form this debate. We have just got to find it. It would be great to have that reported. If someone could compile the cases and report them, I think that would be a pretty powerful case. Is there anyone who objects to this statement in it’s current form? Carried as unanimously.

Equipment

Will Open Circuit Tech Diving Go the Way of the Dinosaurs?

Closed circuit rebreathers have arguably become the platform of choice for BIG DIVES. So, does it make any sense to continue to train divers to conduct deep, open circuit mix dives? Here physiologist Neal Pollock examines both platforms from an operational and physiological perspective. The results? Deep open circuit dives may well be destined to share the fate of the spinosaurus. Here’s why.

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Text and illustrations by Neal W. Pollock, PhD. Header image: SJ Alice Bennett

Evolution is an important force in both the natural and technological worlds. Fundamentally, new features emerge, compete, and the champions face off against the next challengers. The process can be complicated with technology. New products emerge to a reception ranging from enthusiasm to suspicion; a trial period—often long—results in a consolidation of opinion; and successful products gain an increasing market share, although not for long if unacceptable issues or compelling new challengers emerge.

Compressed gas diving has always been reliant on technology. The critical early steps were the effective storage of a pressurized gas supply. Open circuit diving was facilitated by the creation of demand regulators, with the version developed in 1943 by Emile Gagnon and Jacques Cousteau acknowledged as the milestone of modern development. Open circuit diving technology made its way into the civilian community following World War II, and a series of innovations followed to improve utility and safety. J valves were introduced in 1951, offering a simple strategy to hold some of the gas supply in reserve, but imperfectly since divers could fail to set them, they could be bumped into the off position unknowingly, and the rapid increase in inspiratory resistance when they were working could be stressful. 

Submersible pressure gauges appeared in 1958, providing much more information and increased confidence in supply monitoring. Buoyancy compensators appeared in 1961, reducing weighting concerns and improving surface safety. Automatic drysuit dump valves appeared in the early 1980s, simplifying buoyancy control. The line of advanced capability dive computers began in 1983, providing increased information and computational power to simplify dive planning, monitoring, and logging.

Closed circuit oxygen rebreathers also have a long history, with Henry Fleuss credited for developing the first commercially viable one in 1878. World War II provided the impetus for the creation of an array of new oxygen rebreathers, and a growing recognition of the need for equipment to enable safe diving in the range beyond that possible with oxygen systems. 

Electro-galvanic oxygen sensors were developed in the 1960s, expanding the possibilities of mixed gas rebreathers. The Electrolung rebreather was released commercially in 1969, but a high number of fatalities stopped sales within two years. Development through the 1980s was mostly for extreme use in commercial, military, and specialized applications, including science, cinematography, and exploration. The combination of high cost, high maintenance burden, and high training demands made them most appropriate to military and scientific commitment. 

More affordable and user-friendly technology became available in the late 1990s. Draeger released a semi-closed circuit rebreather in 1995. Semi-closed systems conserve the gas supply by allowing some expired gas to be rebreathed while some is lost overboard. They rely on a single gas supply, and the oxygen fraction varies with ambient pressure as it does with open-circuit systems. This technology will not be considered further here.

Peter Readey was developing the closed circuit Prism in the same mid-1990s timeframe, but the watershed event was the release of the Ambient Pressure Diving Inspiration rebreather in 1997. A review of rebreather use in scientific diving from 1998-2013 indicated that Ambient Pressure systems were used for almost 60% of the 10,200 dives logged on 17 different rebreathers by American Academy of Underwater Sciences members.1

Many of the improvements in control, monitoring, and planning helped divers gain comfort in reaching beyond the traditional limits of recreational diving. Open circuit systems provide an open architecture that can be easily expanded. Independent cylinder/regulator/gauge components can be added to provide various travel, bottom, and decompression mixes. The practical limitation becomes the number and bulk of components that a diver can effectively handle—a number that can increase with training, planning, and practice, but only so far.

Are open circuit tekkies staring extinction in the face?
Are open circuit tekkies staring extinction in the face? Image courtesy of SJ Alice Bennett

The term “technical diving” was coined by then aquaCORPS Journal publisher Michael Menduno in 1991 to reflect the complex equipment configurations and practices evolving in the community to expand the diving range. Most of the early efforts were with open circuit configurations, largely due to availability, reliability, and flexibility of the platform. While complex configurations can test diver limits, managing them effectively can also serve as a marker of achievement that is compelling in its own way. 

Perceived Strengths of Open Circuit Systems

Closed circuit technology is inherently more complex than open circuit technology, but the complexity of units designed for the most extreme exposures can provide a misleading point of reference. The design sophistication, reliability, and simplicity of use has continued to advance, particularly for units designed for less extreme applications. The maintenance and operation burden have been substantially reduced, many high-risk and user error failure points have been engineered out or substantially minimized, and the forgiving nature of the units enhanced. It is harder to put units together incorrectly, component reliability has improved, the work of breathing reduced, and internal backups and checks increased.

Fans of open-circuit technology may value the inherent simplicity, but this is compromised by the number of pieces required to accommodate technical diving. The simplicity of individual components may remain, but the collective complexity can be quite high, and the number of individual high-risk failure points substantial. Differences in points of attachment, materials, marking, and mouthpieces can all help to ensure that a switch is made to the right gas, but the possibility of making errors increases as components are added. Every extra pressure line and o-ring also represents an additional point of potential failure.

Additional cylinders add complexity.
Additional cylinders add complexity. Photo by Derk Remmers.

The cost of closed circuit equipment is a barrier, but this too can be misleading. While the initial cost of rebreathers is high, it should not be compared to that of a basic open circuit system, but to the cost of all of the components needed to achieve the desired, if not comparable, capability. This can include multiple cylinders, regulators, harnesses, manifolds, gauges, and the maintenance burden of all.

Closed circuit systems do require time to properly setup and test equipment pre-dive, and a meaningful share of attention throughout dives for monitoring. However, neither the preparation nor monitoring time is out-of-line with that required for complex open circuit technical setups. The ability to check and rely upon a smaller number of pieces of equipment has advantages, particularly as dives become more demanding.

Advantages of Closed Circuit Systems

Closed circuit technology offers some clear benefits to divers. The most obvious is operating cost. While money will be spent in replacing oxygen cells and carbon dioxide scrubber material, a great deal of money can be saved on breathing gas. Gas consumption during open-circuit breathing increases proportionately as a function of ambient pressure, while gas consumption with closed circuit breathing is unchanged by depth. The cost of compressed air for shallow open circuit dives may not be problematic, but the cost of nitrox is high in some places, and the cost of helium for open circuit mixed gas diving is staggering. Divers operating in the depth range of heliox or trimix can see tremendous cost-savings with rebreathers.

A badass-looking Fathom Mk2.5 CCR diver.
A badass-looking Fathom Mk2.5 CCR diver. Photo by SJ Alice Bennett
Gas use in open-circuit systems increases linearly with ambient pressure; gas use in closed-circuit systems depends on metabolic function, which is largely independent of depth.

One of the challenges in diving is that many of the greatest hazards are invisible. While graphic predictions are sometimes provided by dive computers, divers cannot see their actual inert gas uptake or elimination rates or their proximity to decompression or oxygen toxicity limits. Rebreathers do not change this reality, but they can materially change both patterns and hazards. 

Mixed gas rebreathers continuously monitor, and in the case of electronic systems, automatically regulate oxygen levels in the breathing loop in accordance with the setpoint, which is usually diver-designated. A typical setpoint will moderate inert gas uptake through much of the diving range during the descent and bottom phase, and will dramatically augment inert gas elimination and reduce decompression stress during the ascent phase. 

Cave diver sporting the Dive Rite Choptima.
Cave diver sporting the Dive Rite Choptima. Photo by Fan Ping

For example, a setpoint of 1.3 bar/1.3 atm equates to breathing air at a depth of about 52 meters of seawater (msw)/170 feet of seawater (fsw). Using a rebreather with this setpoint at any point shallower favors decompression safety over open-circuit air breathing. The difference is greatest in the shallowest water, which accelerates inert gas elimination during ascent. Considering air as the diluent gas in a rebreather, at 9 msw/30 fsw the nitrogen content would be 0.61 bar/0.6 atm, less than that breathed in air at sea level. At 3 msw/10 fsw there would be no nitrogen in the breathing mix at all. This compares to a PN2 of 1.02 atm breathing open circuit air, which represents a massively less favorable gradient for eliminating inert gas.

The figure depicts change in the partial pressure of oxygen (PO2) and nitrogen (PN2) in open-circuit (OC) with air and a closed-circuit (CC) system running a setpoint of 1.3 bar/1.3 atm. Closed-circuit systems reduce inert gas at shallow depths to optimize decompression. Inert gas loading will be greater at depths where the oxygen setpoint is less than the partial pressure of oxygen in open-circuit gas.

The oxygen setpoint is chosen to balance the risks of decompression stress and oxygen toxicity.2 Electronic rebreathers make continual adjustments to maintain the setpoint, which can reduce physiological stress. Open circuit gas concentrations vary strictly as a function of ambient pressure, which limits the range through which a given gas mix should be used. 

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Switching breathing gases in open-circuit configurations can control oxygen and inert gas levels, but in a very inefficient manner. The need to limit the number of gas switches means that gas fractions are rarely optimized, and can easily approach or exceed accepted safe limits at least transiently, and potentially much more so if the dive profile does not follow the plan. While the research evidence is understandably limited, gas switches may also increase the risk of oxygen toxicity and inner ear decompression sickness. 

The PO2 seesaw, with low PO2 on the left and high PO2 on the right. High PO2 offers both benefit and risk to divers. A reduction in decompression stress is balanced against an increased risk of oxygen toxicity.

A lesser but still important benefit of closed circuit rebreathers is the fact that the gas breathed is warmed and humidified. The warming, a product of the chemical reaction in the carbon dioxide scrubber, can reduce thermal stress, and the humidification both reduces respiratory heat loss and improves comfort. 

Points of Discussion for Closed Circuit System Use

There are several rebreather-related hazards that are not typical concerns of open-circuit divers. Substantial water volumes entering the breathing loop can react with the carbon dioxide scrubber material to produce a caustic foam that cannot be breathed. If oxygen injection into the loop stops, a hypoxic state can develop. If oxygen injection into the loop continues unchecked, a dangerously hyperoxic state can develop. Engineering has reduced the risk of all of these events. Effective water traps make it less likely for substantial volumes to reach the scrubber, and release valves make it easier to clear water from the loop. Oxygen monitoring and control systems are increasingly resistant to failure and provide continuous real-time information to divers to inform divers. 

While some emergency situations can develop quickly, many problems advance slowly with closed circuit systems, allowing divers time to consider options before taking action. Gas supply efficiencies offer clear advantages over open-circuit systems. Real-time warnings can also provide a cushion. For example, not only can divers see current values at any time, dedicated hypoxia warnings are typically activated at 0.41 bar/0.4 atm, almost twice the normal oxygen concentration breathed. This means that the physiological hazard is still a future event. In many cases, modern rebreathers provide the luxury of time to make necessary corrections or, if appropriate, to bail off of the loop and onto a backup breathing system. 

A Divesoft Liberty diver perusing the reef.
A Divesoft Liberty diver perusing the reef. Photo by Martin Strmiska

System engineering has solved many, but not all, issues with rebreathers. Oxygen monitoring technology is reasonably robust, but imperfect, which demands ongoing attention of divers. Carbon dioxide monitoring is still inadequate. While it is generally more difficult to configure systems incorrectly, divers do need to take responsibility to change scrubber material at appropriate intervals. 

Closed circuit rebreathers provide an array of enabling technologies. The economical gas use can make deeper and longer dives much easier to complete, and technical diving computers provide huge flexibility in dive planning and on-the-fly adjustments in plans. The safe range expansion is not unlimited, however. One critical soft limit results from the fact that the decompression algorithms used for deep exposures are developed as extrapolations3 from shallower computations with little or no physiological testing. Mathematical extrapolations from limited shallow water data are unlikely to provide perfect predictions for deeper exposures. They may be conservative, but they may also be liberal. It is critical to remember that math does not equal physiology—ever. A critical hard limit is work of breathing, which increases with depth and gas density. Recent discussion of gas density issues has increased awareness,4 but more effort is needed to ensure that rebreather divers consistently consider both narcotic potential and gas density in dive planning to choose appropriate gases and depth limits.

Arguments have been made that divers should learn open-circuit technical skills before learning closed circuit technical skills. While there certainly has to be knowledge of open-circuit to manage bailout to open circuit situations, it does not follow that one skill must precede the other. Divers can be trained safely in closed circuit techniques from the outset of their diving. This is similar to drivers learning to drive automatics with no manual transmission experience, or pilots learning precision instrument landing approaches without non-directional beacon approach experience. Learning a wide range of skills can be useful, particularly when it reflects a breadth of experience, but it is more myth than truth to say that training in one mode requires foundations in another for safety.

Where is Rebreather Diving Going?

Rebreathers are not a good choice for all divers. They require care in setup and constant monitoring during use. Divers who are not willing to commit the time and effort should stick to the most uncomplicated open circuit diving. A lack of commitment should also discount open circuit technical diving.

Diving is best when it is conducted smartly and safely. While chasing records will always appeal to some, there is probably a lot more pleasure and productivity to diving within skill and comfort zones that are well within the nominal functionality of any piece of equipment used. Rebreathers can offer substantial benefits in reducing decompression stress throughout what we think of as the normal recreational range. They can be used to expand the dive range more efficiently than can open circuit systems, but not without risk. Distance from the surface is important and increasingly unforgiving. A modest expansion of range can provide the best compromise of new experience and safety.

Divers who wish to prioritize gas supply conservation, decompression stress minimization, operational flexibility, and reliance on a single primary platform (with appropriate bailout capability) may wish to consider closed circuit. Those who like technology and value the insights of tracking their status throughout dives will get an extra bonus. 

Those who want to expand their diving range in depth or time should consider the relative merits of investing in and diving with large amounts of open circuit equipment versus potentially more compact closed circuit systems (again, with appropriate bailout equipment). Open circuit technical diving can allow some expansion of the range over non-technical open circuit diving, but operational demands will quickly force a complexity of setup and management obligations that can be problematic. Open circuit technical diving provided an important stepping stone in the development of our diving range,  and will remain important for uncomplicated recreational range activities, but closed circuit technology offers a tool with benefits in the traditional recreational range and clear superiority in the technical diving realm.

Is deep open circuit tech diving destined to share the fate of the spinosaurus? Complete our short OC vs CCR survey to help us find out.

See companion story: GUE and the Future of Open Circuit Tech Diving by Ashley Stewart

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References

  1. Sellers SH. An overview of rebreathers in scientific diving 1998-2013. In: Pollock NW, Sellers SH, Godfrey JM, eds. Rebreathers and Scientific Diving. Proceedings of NPS/NOAA/DAN/AAUS June 16-19, 2015 Workshop. Durham, NC; 2016: 5-39.
  2. Pollock NW. Oxygen partial pressure – hazards and safety. In: Cote IM, Verde EA, eds. Diving for Science 2019: Proceedings of the AAUS 38th Scientific Symposium. American Academy of Underwater Sciences: Mobile, AL; 2019: 33-38.
  3. Balestra C, Guerrero F, Theunissen S, et al. Physiology of repeated mixed gas 100-m wreck dives using a closed-circuit rebreather: a field bubble study. Eur J Appl Physiol . 2022;122: 515–522.
  4. Anthony G, Mitchell SJ. Respiratory physiology of rebreather diving. In: Pollock NW, Sellers SH, Godfrey JM, eds. Rebreathers and Scientific Diving. Proceedings of NPS/NOAA/DAN/AAUS June 16-19, 2015 Workshop. Wrigley Marine Science Center, Catalina Island, CA; 2016; 66-76.

Additional Resources

InDepth: Electrolung: The First Mixed Gas Rebreather Was Available to Sport Divers in 1968 by Walter Starck

aquaCORPS N12: Designing a Redundant Life Support System by William C. Stone (1995) 

InDepth: What Happened to Solid State Oxygen Sensors? by Ashley Stewart

Alert Diver: Do You Know What You’re Breathing? by Michael Menduno

Shearwater Blog: BENEFITS AND HAZARDS OF HIGH OXYGEN PARTIAL PRESSURE


Neal Pollock, PhD, holds a Research Chair in Hyperbaric and Diving Medicine and is an Associate Professor in Kinesiology at Université Laval in Québec, Canada. He was previously Research Director at Divers Alert Network (DAN) in Durham, North Carolina. His academic training is in zoology, exercise physiology and environmental physiology. His research interests focus on human health and safety in extreme environments.

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