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The Making of the Biometric Diver: DAN Europe’s Alessandro Marroni is Realizing a 50-year old Dream

Dr. Alessandro Marroni and his team are preparing to test their real-time diver monitoring system that has been more than 50 years in the making. Called DANA-Health, Sports Monitoring & Advanced Telemedicine, the integrated sensing device, app, and intelligent cloud-service promises to usher in a new era of diving safety and, in the process, pull back the veil from what has long been hidden—what happens within our bodies during a dive. In the interview, InDepth chief Michael Menduno explores the origins and making of Marroni’s brainchild, and reflects on what it may mean for your diving.



By Michael Menduno. Photos courtesy of Alessandro Marroni and DAN Europe. Header image: Alessandro Marroni , at age 18, with a dive buddy ,testing his hand-made underwater compass. Full disclosure: Michael Menduno is a senior editor for DAN Europe.

Ed.Note—Since this story was first published in DEC 2021, DAN Europe has changed the name of its diver monitoring system from ΑVATAR ( Advanced Virtually Assisted Telemedicine in Adverse Remoteness ) to DANA-Health, Sports Monitoring & Advanced Telemedicine.

As this issue of InDepth goes to press, Dr. Alessandro Marroni and a team of researchers from DAN Europe are preparing to test a beta version of their “Advanced Virtually Assisted Telemedicine in Adverse Remoteness” (AVATAR) system in the Deep Dive Dubai pool complex. The real-time diver monitoring system—the brainchild of the pioneering 75-year old diving and hyperbaric doctor and scientist—has been 50 years in the making, ever since Marroni set out the concept in his 1971 graduate thesis, and promises not only to provide a new level of diving safety, but to open up new avenues for diving research. 

As envisioned, AVATAR could be deployed to monitor expedition divers and provide guidance if needed on their decompression should they run into problems. Alternatively, it might be used to assess and recommend treatment for an injured diver on a holiday liveaboard, or serve as an aid to deliver telemedicine services to non-divers engaged in activities such as remote wilderness skiing or trekking.

Dr. Alessandro Marroni in his element at Malta in 2018.

Highly respected throughout the diving, medical, and scientific communities Dr. Marroni has devoted his career in diving and hyperbaric medicine, including publishing more than 250 peer-reviewed scientific papers, to the problems of measuring and collecting diving data, analysis and interpretation, and ultimately to the prevention of diving accidents through better knowledge of their possible root causes. He is perhaps best known by the diving public, of course, for this latter role, as the founder of the organization that eventually became Divers Alert Network (DAN) Europe, in coordination with Dr. Peter Bennett’s DAN US, in the mid-1980s.

The DAN Europe/Comftech smart sensor fabric

The AVATAR system embodies these three themes of Marroni’s career. The system is able to measure a growing number of a diver’s biometrics including heart and breath rate, body temperature, decompression stress, blood chemistry, and other metrics in real-time while the diver is underwater. The system can transmit the data to the surface where it can be monitored and/or sent to an automated cloud data center for processing and analysis and be integrated with an emergency management system such as the DAN 24/7 hotline and diving physician network, and/or an intelligent mission control—more on this later.

While DAN researchers and their partners continue to test and further develop the system, their next step is to productize the AVATAR system so that it can be made available to the diving public. We reached out to Dr. Marroni as he was preparing to leave for Dubai and asked him to explain his vision and the making of the AVATAR. Here is what he had to say.

InDepth: I watched one of your talks on Zoom and saw the plaque on your desk with a quote from Walt Disney, “If you can dream it, you can do it.” Those seem to encapsulate the story of AVATAR just perfectly.

Alessandro Marroni: Well, that is simply my life philosophy, to just follow your visions, and firmly believe that a winner is just a dreamer who never surrendered. [Marroni smiles]

Obviously, you have never surrendered! I was amazed to learn that you first dreamed of what is now AVATAR 50 years ago, while you were a medical student and published your graduate thesis in 1971 titled,  “Esplorazioni di monitoraggio cardio-cerebrale nel nuotatore subacqueo.” In English: “Exploring cardio-cerebral monitoring in the underwater swimmer.” What inspired you to choose that as your thesis topic? 

Well, I was already a diver and a diving instructor—I learned to dive at age 13 and became an instructor at 19. I worked as an active instructor during my medical studies and was looking for a thesis topic. 

The cover of Marroni’s 1971 thesis

At that time, I was a resident in clinical medicine at the University of Bologna, and my mentor Professor Giulio Sotgiu, who is listed on the thesis as my mentoring tutor, was a cardiologist and very involved in monitoring sports activities. I told him that I wanted to go into diving medicine; I had known since the beginning of my studies that’s what I wanted to do.

Professor Sotgiu had developed a system to monitor heart frequency using light transmission through the soft tissues, and he suggested that we apply this to divers. At that time, there was no wireless through-water transmission, so the diver was tethered to the surface. From there we could actually see the subject’s heartbeat and heart rate frequency that was transmitted with light signals. It was just natural and seemed like an obvious thing to do.

Since that time, you have spent years monitoring and taking physiological measurements of divers, not just before and after dives but while they were actually underwater. You have recorded heart functions, taken bubble readings, measured hydration, drawn blood and measured blood chemistry. Why is it important to monitor divers during the dive, as opposed to just before and after?

What happens in a diver before and after a dive has been extensively studied; however, that’s not the case when they are underwater. Further, our field research has shown that some variables, like the production of nitric oxide (NO) for instance, may seem not to change before and after the dive, but when we took blood samples during the dive, we could observe very significant changes. This is just one example that however bears some implications, since this substance is related to the function of the endothelium, and this is related to the response to and formation of gas bubbles. Further research has shown that such changes of the endothelial function, or specifically irritation of it, can also be identified by monitoring heart function.

 Are you referring to recent work on heart rate variability?

Yes. There is a study that we are doing with the University of São Paulo in Brazil about heart rate variability. The scholar and researcher we are cooperating with is Sergio Schirato, who is a specialist in cardiology as well as a diver. 

Yes, Dr. Schirato wrote a story for us last year  titled, “Heart Rate Variability: What it is and Why it Matters.
Conducting an electrocardiogram on a plane as part of a DAN Europe flying after diving study in the early 2000s.

He is part of our multinational team, and he has developed a modality to interpret the endothelial stress from certain variables in heart rate. It so happens that the estimation of the endothelial stress matches with our estimation of decompression stress in post-dive bubbles. Which means that we could have an early marker for decompression illness (DCI) if we want to verify heart function underwater. 


Another example is exercise. It was always believed, and has been retrospectively assessed, that parameters such as exercise have an influence on human response to decompression, and the level of exercise can be monitored through respiratory and heart rates. The same applies to certain environmental parameters, such as temperature. So, the ability to monitor divers in real time while they are diving, can provide key insights into what’s happening, and that data can be analyzed using tools like DSG, the Diver Safety Guardian—our decompression risk analysis model, for example—and the results can be used to say, modify their decompression plan. The software is contained in our water tight Dive Sense device.

So, a diving supervisor could monitor their expedition divers, for example, and advise the divers and make changes to their deco plan, depending on their physiological status. 

Exactly. We could compute what would be the best ascent for the diver taking into account, for example, their heart and respiratory variables.

Wow. That’s exciting. You mentioned your start monitoring the cardiac functions of a tethered diver for your thesis. I read that you also worked with freediving pioneer Jacques Mayol back in the 70s, taking subsurface measurements on his record dive to 86 meters.

Yes, I was measuring his heart rate and also his mental performance with some visual and manual coordination tests. I used a small pegboard, where you have to insert the peg into the proper hole. It’s something childlike, but very effective. I took measurements during his training period.

Dr. Marroni taking Jacques Mayol’s pulse at 86m/281 ft

On the record dive, he allowed me the time to measure his heart rate. But on the other training days, he made dives close to the 86 m/282 ft; we were diving every day between 75 and 80 meters. He gave me time to do all these tests—both the mental and the psychomotor coordination tests, and heart rate. At that time, the instruments available were not as sophisticated as  they are now. In fact, that’s where I began the move towards digital medicine—I actually measured his heartbeat with my digits. [Dr. Marroni holds up his fingers and laughs!]

Dr. Marroni conducting a coordination test with Jacques Mayol at a depth of 50m.
Digital medicine, right? Ha! It seems obvious that we’d want to monitor divers’ physiology during the dive. The problem is that it has been difficult to accomplish that underwater. 

That’s right. If there’s no water, everything is simple. That’s why I wanted to develop the system for use underwater, even in space. If you can do something underwater, you can do it everywhere. Of course, with Jacques Mayol, conducting manual tests was the only thing I could do. But things continued to evolve. We were hungry for data, and we began developing new systems and approaches. 

We put a Doppler probe in an underwater case so that we could actually monitor bubbles at the bottom and during the ascent. We put echocardiographs in a pressure-resistant case so we could actually do underwater echocardiography. Eventually, we started drawing blood underwater. So, the next step was obviously to develop modalities to monitor any other physiological function underwater. This is where the Avatar concept started taking off. 

  • Buddy Dive Bonaire

Clearly the development of biometric technology and availability of wearable sensors has helped a lot. We started working with existing technology and adapting it to the underwater world. But we had a problem. The problem was that having a tethered sport diver was not so easy or comfortable. So, we had to overcome this issue. 

How did you do that?

We had the great opportunity to partner up with Newcastle University in the U.K. We had been introduced to them through an important project that we got involved in called Cognitive Autonomous Diving Buddy (CADDY). Basically, we developed an underwater robot or ROV that could monitor and interpret the hand signals and body language of a diver together with other physiological parameters. Newcastle had developed a very smart underwater signal transmitter using ultrasound and acoustic modems as part of the project, and we cooperated with them.

We were conducting a diabetes monitoring study—we were actually monitoring blood glucose in diabetics underwater. A display would show both the diabetic diver as well as the instructor the diver’s blood glucose level. The idea was that real-time monitoring would enable a diabetic diver to know what was happening to his or her blood glucose during the dive, so that they could take appropriate action. The result was a very nice paper with a protocol that would allow diabetic divers to dive more safely, and also included this real-time monitoring of the blood glucose level during the dive, not only before.  

Initially, we were using Bluetooth to do this. But underwater, Bluetooth doesn’t go more than 20 to 30 cm (8-12 inches), and so the poor diver had to place the monitor very close to the subdermal transmitter to see the display. That was obviously not so practical. But Newcastle showed us how to transmit signals using ultrasound and acoustic transducers. The effective range was up to three kilometers or about two miles if you have a line of sight, which is very easy underwater. 

That was the breakthrough! It enabled us to capture the signals from wearable sensors on the diver and transmit them to the surface with an acoustic transducer, essentially an acoustic modem. From there, of course, with a good antenna and GSM (cellular) or satellite connection, you can transmit the data anywhere in the world. So that moved our project forward, and my youthful vision and dream started to become a reality.

It’s another key component of the AVATAR system.

We also had a great opportunity to meet with Comftech, a company based in Milano that developed a very novel technology, a textile technology that actually collects data, and can then transmit it through a small Bluetooth transmitter. The Bluetooth signal is sent to the acoustic modem that is worn by the diver on the wrist like a dive computer, and then the acoustic modem transmits it to the surface. That opened up a whole new world. These intelligent textiles can collect electrocardiogram, temperature, respiratory rate, geolocation, and body position data by using an accelerometer—whether its heads up or down, or horizontal, or falling. 

Dr. Marroni with Pierre Yves Cousteau who participated in the research and helped to promote DAN Europe’s Diving Safety Lab research camps in the early 2000s.
That was part of the DAN demo that you showed me. A diver surfaces from a repetitive afternoon dive on a liveaboard in the Maldives and he is not feeling good. So he puts on the DAN monitoring shirt, connects to his phone app and calls DAN. He is then connected to a diving physician that can read his biometrics as well as the dive profile from his computer, and can diagnose him and recommend treatment. Amazing! 

It was a natural evolution for us to begin to collect diving data in addition to the accident data which we were already collecting. This is something that I started with Dick Vann and Petar Denoble, who were then at Duke University and DAN US back in the early 1990s. 

We worked with many computer manufacturers to essentially include a “Send Data To DAN” button on their devices to put together what is now the data collection system that DAN has and shares. On the European side, we have the Diving Safety Lab, which as you know, has become part of the Avatar system. DAN US had the Project Dive Exploration data. 

In addition to the dive profiles, we collected information about the diver through a questionnaire, which is conducted after the dive. The questionnaire includes information on their habits and what happened to the diver before the dive—whether they were rested, or unrested, had slept, had drinks, smoked and so on. That allowed us to collect a large amount of data for epidemiological research.

We also started running field research camps in 1993 where divers could participate in organized field research. We invited DAN members to participate, and we continued to collect data. During my early days working as a commercial diving doctor, I acquired Doppler recording units shortly after I worked with Mayol. I routinely used these Doppler probes with my commercial divers, and it was natural to start using them on recreational divers. They were the very first tool that we used during these camps—what we called the Diving Safety Lab research camps—and we continued to collect data before and after the dives. 

Eventually, we focused on three assessments. One was the Doppler assessment, post-dive, with a certain protocol. The second one was hydration—we measured hydration through urine density before and after the dive. In addition, on many occasions, we also measured blood density with a small pin prick amount of blood that we processed for hematocrit and hemoglobin. That allowed us to analyze a serious amount of data. We published the first results in 2000 and published our last study about diving risk factors about four years ago, based on 40,000 dives. See: Alert Identifying Decompression Risk Factors

I know that you used the Dive Safety Lab database to develop your decompression risk analysis model among other things. Let’s talk about the third component of the AVATAR system, mission control, and the DAN emergency management system. 
Your first job out of medical school was as the diving medical officer (DMO) for the Italian national oil company, Eni SpA (Ente Nazionale Idrocarburi.) And that, in fact, led you to create what eventually became DAN Europe.

That’s right. I first worked with Eni while I was resident at the Institute of Occupational Medicine at the University of Genoa from 1972-74, and then I

became the medical director for their underwater work when I left the university. I was involved in all of their commercial diving activities for more than 10 years until 1985. In fact, I shared one of my experiences from that period in Stratis Kas’ book “Close Calls.” 

I remember that story!

Eni was conducting compressed air dives to 50 m/165 ft, but also starting to work with artificial breathing mixtures for deep bounce diving, as well as saturation diving. We did some of the first deep bounce diving with heliox, using a diving bell and umbilical, and also the first saturation dives.

Now, in the late 70s and early 80s, European diving was booming with the advent of dive travel and dive destinations like Sharm El Sheikh and the Maldives were busy. Predictably, incidents of decompression illness (DCI) were also on the rise.  I was already an active PADI instructor, having done my cross over from CMAS with Steve Metcalf. 

At the time the idea of providing the recreational diving community with the same type of assistance we were providing to commercial diving teams worldwide was just a natural development of my work. I was doing telemedicine, we had 24/7 phone assistance, dispatching teams, and arranged air evacuations, and so on.  

So in 1980, I started envisioning the program, which then began in 1982 as  International Diving Assistance, or IDA, with an international 24/7 hotline to provide guidance to injured divers regarding treatment in the few chambers that were available in those early years. I was later helped by my wife Nuccia and a small network of like-minded diving physicians to further develop IDA, and to add a diving insurance program.    

The components of the AVATAR system.

I was already a member of a number of scientific societies. I had served as the president for European Underwater and Baromedical Society (EUBS), vice president of Undersea Hyperbaric medical Society (UHMS), and we had started the European Committee for Hyperbaric Medicine (ECHM). So, it was natural for me to ask my friends and colleagues, “hy don’t we build a European network?” And that is how we built the multilingual, multinational DAN Europe network.

That was the beginning of what would become the Divers Alert Network (DAN). Of course, in parallel, Dr. Peter Bennett, from Duke University had set-up a diver hotline in 1980 in the States called the “National Diving Accident Network” divers’ hotline (NDAN) with grants from NOAA (National Oceanic and Atmospheric Administration) and NIOSH (the National Institute for Occupational Safety and Health) to address the needs of recreational diving.

Yes, I met with Peter, who was also involved in saturation diving research at a conference in Aberdeen, Scotland, in the late seventies. I knew what he was doing, and he knew I had similar aims.

Later in 1986, you and Bennett decided to collaborate and form two independent Diver Alert Network (DAN) organizations: DAN Europe and DAN US. 

I had started operations as IDA, then agreed with Peter to also adopt the name DAN followed by “Europe.”  Around that time, it began to dawn on me that I was interested in pursuing research and teaching, and I left Eni a few years later, and began teaching at University of Chieti in Abruzzo, where I live now, and of course concentrating on my work with DAN. 

  • Buddy Dive Bonaire

As we talked about in the example of a liveaboard diver getting bent,  the AVATAR system can easily be integrated in DAN’s emergency network for treating incidents. But you have another larger vision. You see AVATAR being integrated with an automated, cloud-based mission control function.

Yes, that came out of our work with a company called Altec, which is part of Thales Alenia Space that works with the European Space Agency (ESA). Altec is the company that actually built the International Space Station (ISS) modules, and they maintain a mission control for the technical aspects of the ISS in Torino; they are connected to the ISS all the time. 

Altec sponsored and helped us greatly with the AVATAR concept and developing an intelligent mission control function that would collect the data coming in from divers, analyze and interpret that data, and if warranted, report the situation to a human mission control that could reach out to the diver, and so on. This led us to the concept of ‘bidirectional telemedicine.’ 

An illustration of bidirectional diver telemedicine

Telemedicine is usually done over the phone, but of course, it can now be done with videoconferences. You can look at the patient and provide [virtual] assistance using the physiological or pathological data, including visual data, that comes through the system to a mission control, which is made up of two parts. 

The first is an automated mission control, very much like you would have in an intensive care unit, that displays heart signals, lung signals, breath rate, and so on. If certain thresholds are reached, either high or low, an alarm would fire. So, in the case of a diver, this could apply, for example, to someone diving with heart problems or something like that. If the alarm fires, then the human alarm center is alerted, and a search and rescue operation could be started, or at least the diver could be notified that there is a problem. 

The second part of the system was providing feedback to the diver. Using the GSM network and acoustic modems, we realized that 

we could send back signals to the diver underwater. We developed a modality to actually send text messages, which require minimum bandwidth. So, we started using coded messages that would mean, how are you? Are you okay? You’re not okay. Remember I showed this to you in the simulation of a diving accident. 

Yes, I remember that demonstration.

This is bi-directional telemedicine because we now have the opportunity to actually send some feedback to the remote diver or patient. Of course, in the case of an injured diver at the surface, a physician could speak with them directly through an app. 

It could also be used to communicate with a bystander that was helping the diver and could benefit from the knowledge and experience of a remote specialist—they would essentially become an onsite avatar of the remote specialist. In the case of the ISS, for example, Altec have systems that can guide an astronaut, via video and augmented reality, to fix an electrical panel on the ISS. 

Wow! The future’s so bright, I gotta wear an Oculus Rift!

Our challenge now is to develop some sort of visual guidance, which would use augmented and virtual reality to show a bystander how to help the injured diver. That is the next step. We are not there yet. We are pretty happy where we are at the moment, and with being able to communicate with our diver with coded signals. 

The good thing is that, as I showed you, the system now allows us to monitor the dive during the descent and ascent, with automatic feedback, say every five meters, that displays data about heart and respiratory rate, and also decompression-related data. With that, our Diver Safety Guardian system is able to do real-time decompression risk analysis, and also to understand what would be the best ascent given the divers descent and bottom time.

A brave new world. So what’s next? What are the next steps going forward?

The next steps are to make AVATAR available to the public. Obviously, we will need to industrialize it, and we will need to make it available at affordable costs. It shouldn’t be something that only Elon Musk can afford, but something more basic like a normal Chevy or Ford. We also aim to integrate AVATAR with current dive computers, because it’s not a dive computer. Rather, it will take data from the environment, from the diver, from the dive computer, and then integrate them into a meaningful stream of data. It would be the diver’s advisor, his or her guardian angel. 

The system would enable the diver to be in contact with a remote expert, which could be an automated expert, because we are working with artificial intelligence. If the diver chooses, they can be in constant contact with an automated mission control, sending data to a central database that would be able to provide feedback if something goes wrong—to fire an alert signal, for example. It’s not a far-fetched goal, because this is already in the prototypes that we are using.

The Dive Sense device is an important component of the AVATAR system
Do you plan to team up with commercial enterprises to help productize the technology?

Most probably yes. DAN is a foundation that provides service and insurance. It is not a manufacturer. So, we will likely partner up with companies that can help us. I see it more as an intellectual property and opportunity that we offer to the diving community. If there are manufacturers that are ready to come on board and also share the benefits, so much the better.

On the other hand, one thing we are very proud of is the portal that serves as the repository of divers’ data, a kind of clinical record of the dives. That is something that, for sure, DAN will retain because that is part of our assistance mission. The monitoring tools, the integration of existing sensors into the system and so on, are all simply a smart use of the existing technology.

In a recent talk you said Avatar will make a difference. It will make it possible for DAN to be ever more of a dive buddy. 

Yes. Not if, and not even when. This is now a reality and only needs to be industrialized to be made available. DAN will end up being a dive buddy, not only before and after your dive, but even when you are diving.

It seems to me that AVATAR represents a major paradigm shift, enabling us to pull back the veil and see what’s happening to a diver throughout the whole dive. That’s something that has only been done in pieces before. It seems very powerful.

AVATAR will be extremely important for research because it unveils what has been veiled so far—and that is what happens during the dive. What happens before and after has been extensively studied by many. What happens during the dive has been barely studied, in certain very advanced military environments, but is not done anywhere else. Definitely not in commercial diving environments, even less in recreational diving environments. We are essentially applying technologies that are common in space medicine today—astronauts are monitored this way. 

We want to make this kind of technology, and real-time monitoring, which can be very useful in terms of knowing how your body is responding, and alerting the diver to potential problems, available for the diving public.

It’s a powerful vision Dr. Marroni. Let us know how your tests go at Deep Dive Dubai. And please keep on dreaming!


  1. IDA’s operations began in 1982. In 1986, Marroni agreed with Bennett to adopt the name Divers Alert Network (DAN), followed by “Europe,” while Bennett also modified the DAN name from Diving Accident Network to Divers Alert Network. Then Prof Hioshihiro Mano who had started CAN (Civil Alert network) in Japan, John Lippman, who ran DES ( Diving Emergency Service) in Australia, and later Dr. Frans Cronjé from South Africa, joined the vision and in 1990 they formed International DAN, a federation of independent organizations sharing same vision, mission and operative modalities. These were DAN, DAN Europe, DAN Japan, DAN Australasia and DAN South Africa.

Dive Deeper:

Alert Necessity, The Mother of Invention: The Story Behind DAN Europe’s Diving Insurance

Facebook (2019): Introducing the diving #avatar. Prof. Alessandro Marroni speaks about the research tests currently being held to implement an innovative system

Frontiers: Dive Risk Factors, Gas Bubble Formation, and Decompression Illness in Recreational SCUBA Diving: Analysis of DAN Europe DSL Data Base

Michael Menduno/M2 is InDepth’s editor-in-chief and an award-winning journalist and technologist who has written about diving and diving technology for more than 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, and he produced the first tek.Conferences and Rebreather Forums 1.0 & 2.0. In addition to InDepth, Menduno serves as an editor/reporter for DAN Europe’s Alert Diver magazine, a contributing editor for X-Ray mag, and writes for He is on the board of the Historical Diving Society (USA), and a member of the Rebreather Training Council

Tags: V 3.12, DAN Europe, decompression, risk analysis, biometrics, real-time monitor, Doppler


InDepth’s Holiday Rebreather Guide: 2022 Update

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, the Guide features 28 models of back, chest, and side-mounted rebreathers, including two new entries, for your shopping operation. So, get out your pre-buy checklist, and that gift certificate and start ogling your loop of your fancy. Ho ho ho!




InDepth’s Holiday Rebreather Guide: 2022 Update

by Michael Menduno, Amanda White and Kenzie Potter

Holiday images by Jason Brown, BARDO CREATIVE

1DEC 2022—Ho ho ho! Once again, we have updated InDEPTH’s Holiday Rebreather Guide adding two new rebreathers; the new Gemini sidemount mCCR from Fathom Systems, and the generic breathing Machine (GBM) back mounted eCCR 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!

17DEC2021: 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!

Sport diving rebreathers have come a long way since storied explorer Bill Stone trialed his 80 kg/176lb fully-redundant “Failsafe Rebreather For Exploration Diving” (F.R.E.D.), and spent a cool 24-hours underwater as part of his paradigm-shifting 1987 Wakulla Springs Project. In retrospect, looking back over the last 30-some years, the “Technical Diving Revolution,” which emerged in the late 1980s to late 1990s, was ultimately about the development and adoption of rebreather technology. 

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 (22JUL2021): 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 (9DEC2020): 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.

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!!

Ed. 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)

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.

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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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