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Are we there yet?

Rebreather technology for recreational divers.




From May 18-20, 2012, experts from around the world will gather in Orlando, Fla. for Rebreather Forum 3 to re-examine the state of rebreather use and develop protocols and recommendations to improve user safety. This program will be co-sponsored in part by DAN, PADI and the American Academy of Underwater Sciences (AAUS), featuring rebreather specialists, experts, manufacturers, training and education leaders, scientists and dive safety researchers. The weekend is open to anyone with an interest in rebreather diving and technology, and several registration options are available.

"In the future, you'll simply jump into your car, turn on the Internet, turn on a movie and sit back and relax and turn on the automatic pilot, and the car will drive itself," says Michiko Kaku in his book Physics of the Future. "Unlike a human driver, it doesn't get drunk, it doesn't get distracted and certainly does not have road rage."

Even though driverless cars are not yet commercially available, driving a car is a simple process with all of the complex technology hidden from the user. Today's rebreather technology is a few steps behind, but it may be catching up.

Sixteen years ago diving scientists, manufacturers, divers, training agencies and regulators met for three days at Rebreather Forum 2.0 (RF2.0), in Redondo Beach, Calif., to discuss the future of "sport rebreather diving." At the time, at least one dozen rebreather models had appeared on the market, some of which were there to stay. The market was minuscule, and training opportunities were practically nonexistent. The consumer base consisted of about 100 brave, knowledgeable divers who recognized they could achieve more in their respective fields using rebreathers but at the cost of more work, money and risk than average divers were ready to commit.

RF2.0 reviewed the physiology of rebreather diving and the enabling technology, including the risks and needed enhancements if sport rebreather diving became popular. The findings and recommendations of RF2.0 emphasized the complexity of closed-circuit rebreathers (CCR), a need for technical support and better control of insidious risks including hypoxia, hyperoxia and hypercapnia. Additional safety issues were also noted such as a "caustic cocktail," an unanticipated variation in the partial pressure of nitrogen, thermal considerations and mechanical or electronic failures. Some technological advances were explicitly required, like full-face masks to prevent drowning in case of unconsciousness and an on-board carbon dioxide monitor to prevent carbon dioxide poisoning. Third party pre-marketing testing was advised, but standards were not proposed.

When compared to open-circuit scuba, rebreathers required significant ongoing maintenance and support to function properly; the consensus among the forum attendees was that rebreathers were suited for the technically savvy rather than the average diver. Military divers have successfully managed the risks of using rebreathers with resources not available in sport diving, including the use of a large supporting infrastructure, a high degree of discipline and extensive formal training.
Changing Tides: RF2.0 to RF3
Dr. Richard Pyle describes the experience of a self-taught rebreather diver best: "After my first 10 hours on a rebreather, I was a real expert. Another 40 hours of dive time later, I considered myself a novice. When I had completed about 100 hours of rebreather diving, I realized I was only just a beginner."

He did, however, provide a few survival tips for new rebreather divers:
  1. Know your partial pressure of oxygen (PO2) at all times; do not trust "fail-safe electronics."
  2. Learn, in depth, diving physics and physiology.
  3. Training should emphasize failure detection, manual control and bailout procedures.
  4. Cover your ass (have a back-up).

The experiences and tips of Dr. Pyle and his peers became the basis for development of formal training for technical rebreather divers.

But there were additional challenges for the trainers. According to Karl Shreeves, technical development executive for PADI worldwide, before the training agency could consider the instructional system, it was necessary to determine who the customers would be and how they would use rebreathers. PADI considered rebreather diving a niche not of interest to mainstream recreational divers at the time, but recognized the trend could change at any point. Indeed, a lot has changed; rebreather technology has improved, some training agencies have started offering instruction and the number of users has increased from hundreds to tens of thousands.

The fatalities have also risen accordingly to more than 20 per year, or more than 190 in the sixteen years since RF2.0. Not all of these fatalities were rebreather-specific, but all analyses indicate operator-machine interaction played a major role in it. It's an interaction that must be acknowledged, understood and made as safe as possible. Dietmar Luchtenberg of Europe's Rebreather Advisory Board said, "We can't get rid of safety issues in rebreather diving by [only] increasing technology standards." He emphasized the need and challenge of eliminating the factor of human error to enhance diver safety. After RF2.0, there was also a consensus about the significance of the human factor in the safety of rebreathers; the suggested approach seemed to be to develop a reasonably safe device and shift the residual risk to the users.

Rebreather diving is still a technical-diving niche, but it seems ready to spill out into the mainstream of recreational diving. As the industry prepares for this shift, we wanted to know what has changed in rebreather technology since RF2.0 that gives the manufacturers a confidence to sell it to mainstream recreational divers, on what premises training agencies built their instructional system, what kind of support the instructors are counting on, and what possible hurdles and achievements an independent rebreather expert may foresee in the near future.

What has changed since RF2.0 that helped PADI decide to provide CCR courses?

Karl Shreeves: Several significant changes have occurred since RF2.0 that made it appropriate to begin offering rebreather instruction on both the recreational and technical levels. These changes include:
  • The debut of computer-controlled Type R (recreational) rebreathers intended for no-stop diving by mainstream divers.
  • The nearly universal acceptance of enriched-air nitrox for mainstream diving and the growing acceptance of rebreathers in technical and recreational diving.
  • A trending shift away from open circuit in deep technical diving and a rise in the proportion of divers using rebreathers.
  • The growing number of dive boats, resorts and centers offering the appropriate support.
  • An increase in the sophistication of rebreather design and technology, including oxygen sensor performance, carbon dioxide sensors and rebreather computing.

Open-circuit scuba will likely remain the mainstay in recreational diving and technical diving shallower than 131 feet. It has a long-standing track record of reliability, simplicity and access. However, with the improvement in rebreather technology and the rise in units now available, the time has come to offer comprehensive, responsible training for the growing number of divers interested in using them.

What kind of selection would you like to see for recreational rebreather trainees?

Dr. Douglas Ebersole: There are three aspects that need to be considered here. First and foremost is the mindset of the potential student. They need to be responsible divers who show good judgment, are not impulsive and pay attention to detail. They must demonstrate adherence to a checklist, an imperative safety measure even for a recreational rebreather.

Second, there is the academic knowledge needed to be a safe recreational rebreather diver. For recreational, no-decompression CCR diving this would be a nitrox certification. The student needs a good understanding of partial pressures of oxygen and nitrogen at various depths with varying nitrox mixes.

Finally, there are the skills needed. The addition of counterlungs and the inability to control buoyancy with inspiration and expiration makes buoyancy control more difficult on a CCR than open circuit; therefore, a good open-circuit buoyancy control would be a very important prerequisite prior to beginning CCR training.

What tasks and in what conditions will recreational divers use CCRs?
Shreeves: Recreational divers use rebreathers for the same tasks and in the same conditions they use open-circuit scuba. The primary benefits are optimized decompression resulting in longer dive times, silence for superior aquatic life interactions and the comfort of breathing warm, moist gas.

Technical divers use CCRs to enable increasingly deeper and longer dives than are possible using open circuit. Although most cave diving will likely remain open-circuit, exploratory cave divers will increasingly use the technology for long penetrations and in caves so fragile open-circuit bubbles could be damaging.

What level of logistical support do you expect the industry will provide?

Shreeves: Many dive centers and resorts are already providing rebreather support, and it should become more common. Both recreational and technical rebreather diving require specific support elements to be a feasible option.
  • Supply cylinders, bailout cylinders and absorbent at dive destinations.
  • For technical CCR diving, trimix diluent and bailout gases.
  • Boat trips oriented to accommodate the greater durations (and for technical divers, depths) associated with rebreather diving.
  • A dive operation staff with the appropriate training and experience in rebreather diving.

What kind of organizational support for instructors and trainees would you like to see?

Ebersole: A manufacturer-provided waterproof checklist would emphasize the need for adhering to checklists before diving a rebreather. In addition, manufacturers and training agencies should offer continuing education to instructors and divers alike to keep up with this rapidly evolving field. Ideally, this would be web-based to allow access 24/7 around the globe. Finally, manufacturers and training agencies need to strive even harder to have the highest quality instructors. They should emphasize that instructors of various units should not just be certified on these units, but actually dive with the particular unit regularly. Agency-required evaluation forms by students should also be submitted directly to training headquarters and the rebreather manufacturer to facilitate quality control.


Are we already at the stage where complex technology can be placed "under the hood," creating a rebreather rig that is reliable, safe and simple to use?

Dr. Yochanan I. Daskalovic: Since the 1990s, most rebreathers - and especially ECRs (electronically-controlled rebreathers) - were developed and constructed by individuals and small enterprises; now a few larger companies have introduced some well-constructed and more reliable ECRs.

However, compared to open-circuit scuba, they are still quite complex and complicated machines, with higher costs, a need for elaborate pre- and post-dive preparation, maintenance, different user training, and a much more thorough knowledge and understanding of the physiological principles and hazards involved. Thus, they may be safer and somewhat simpler to use than their predecessors, but they are still a complex machine not for the neophyte diver.


What safety solutions must be implemented with the introduction of a "recreational rebreather?"

Ebersole: For a recreational rebreather there should be one solution to any problem: bailout to open circuit. Along these lines, a bailout valve should be an integral part of any recreational rebreather design, so with "the flip of a switch," the diver is immediately on open circuit. For simplicity, the unit should have an adequately-sized diluent cylinder to enable a diver to safely reach the surface with a safety stop from recreational depths. This would avoid the need to carry additional bailout cylinders, which requires additional skill sets.


What should be done to further reduce end-user risk to levels manageable for mainstream recreational divers?
Daskalovic: When we talk of risks involved in the use of rebreathers, we should remember that as with any activity involving the use of a machine (mechanical and/or electronic), the more complex the machine is the more difficult and time consuming it will be to learn to operate and maintain it, and the more prone it is to malfunction. Thus, it has to be as user -friendly with the simplest man-machine interface possible.

Training in the use of rebreathers should start as early as possible in the educational process of a student diver; it should not require proven experience and certification in open-circuit scuba; veteran divers sometimes have more trouble getting used to closed-circuit diving breathing and buoyancy control than novices who never dived with open-circuit scuba. Moreover, starting training with a simple mechanical rebreather before advancing to ECRs will also simplify the learning and may reduce the user's risks.

However, even with the best diver training (including the proper responses and bailout techniques in case of some malfunction), reliable mechanical and electronic components along with good physiological rationale incorporated into the rig's algorithms and controllers are essential for a dependable ECR. The above, plus quality and simple human engineering will minimize user error in case of emergency.

What would it take to create a "driverless rebreather?"

Daskalovic: Although it may be the dream to have a "driverless rebreather," it does not seem to be attainable in our lifetime and probably not ever. Whereas a car is a vehicle that takes us from one place to another in our familiar terrestrial environment, a rebreather is essentially a life-support system used in a foreign aquatic environment. In the case of an emergency, there are too many variables that must be controlled, and response times are critical.

However, there are some requirements that should be incorporated into the optimal rebreather/ECR:
  • Fail-safe mechanical and electronic components.
  • -Accurate and reliable oxygen sensors (the current galvanic sensors are mostly unreliable)
    -Accurate and reliable carbon dioxide detector (currently only two manufacturers claim availability; one is in a military unit in its final prototype)
    -A built-in decompression meter taking into account real-time oxygen partial pressure values based on a field-tested and verified algorithm (similar to tests performed by the U.S. Navy on their VVL-18).
  • A dual-redundancy gas control system: In case of partial or total failure of the gas control and/or injection systems, a mechanical controller will take over automatically; this will enable safe completion of emergency procedures and decompression requirements.
  • A reliable continuous visual heads-up monitor and audio alarm system (currently today).
  • An open circuit bailout system for critical emergencies like counter-lung flooding, where no controlled constant PO2 ascent may be possible (available today).

There is, and most likely never will be, no substitute for thorough training in and understanding the complexities involved in ECR diving. The human driver always will have to be in control. We believe the mechanical valve can make a positive contribution to the inherent safety of the ECR currently under construction by providing a means of operating at depth under a variable workload sustained by the oxygen and diluent mixtures on-board the ECR. This constitutes a significant improvement over the currently available abort options.
Meet the Experts
Karl Shreeves, technical development executive for PADI Worldwide. He has been interested in diving since he was a child and was first certified in 1970. Shreeves became an instructor in 1985. He is currently a PADI Course Director. In 1991, Shreeves began technical diving with the Farb Monitor Expeditions. He did his first rebreather dive in 1994 at Rebreather Forum 1.0. Since then, he has dived many different CCRs and semiclosed rebreathers and is fully certified on five rebreather models.

Douglas Ebersole, M.D., was certified in 1974 and became an open water instructor in 2002. He began technical diving and diving rebreathers in 2003 and is currently an International Association of Nitrox and Technical Divers and Technical Diving International Closed-Circuit Rebreather Trimix Instructor. He is able to teach six different semi-closed and closed-circuit rebreather models. He is also a Florida Sales Representative for the Kiss SCR and CCR Rebreathers. When not underwater, Doug is an Interventional Cardiologist at Watson Clinic and the Director of the Cardiac Catheterization Laboratories at Lakeland Regional Medical Center in Lakeland, Fla.

Yochanan I. Daskalovic has been developing and testing rebreathers for the last 40 years. He has a Ph.D. from the University of Wisconsin-Madison in physiology with emphasis on respiration, diving, environment and exercise. In March 2009, he retired from the Israel Naval Medical Institute where he served as a diving physiology researcher for 27 years. He has worked in research and development of life support systems used in diving and their physiological evaluation. He has played a key role in the development and evaluation of two prototypes in electronic rebreathers over the last 10 years. He continues to work as an independent research consultant.