Closed-Circuit Rebreather
Training Guide

I wrote this guide from the perspective of a sport and technical rebreather diver and instructor. My name is Mark Derrick, and I am based in Pompano Beach, Florida. I earned my first rebreather instructor rating in the late 1990s and teach several CCR platforms, including the Poseidon Se7en+. I am currently a staff instructor at Dive Gear Express.

Closed-circuit rebreather is a form of scuba diving equipment that recycles breathing gas rather than venting it as bubbles. CCR is generally appropriate only when open-circuit diving has become limiting in terms of gas supply, depth, or efficiency, and you understand why. If you are early in your process of researching the idea of diving with a rebreather, you could start by reading Basics of Rebreather Diving by Jill Heinerth.

Key Advantages of Rebreathers

• Silence - A closed-circuit rebreather produces almost no bubbles, and the resulting silence can materially improve the dive because marine life are less alarmed by the diver. If you are a photographer or marine scientist, the silence of a CCR can significantly improve marine life interactions and photo opportunities.
• Extended Ranges for Depth and Time - A CCR can provide breathing gas duration that is largely independent of depth, so dive time is no longer limited by the size of the tank. A rebreather can also greatly extend no-decompression limits for sport divers. If you are a technical diver or overhead-environment diver, then a CCR often makes practical sense.

Key Disadvantages

• High Cost - There is a wide price range, but the cost to become an eCCR diver is typically many times that of an open-circuit diver. Consumables in remote destinations can also be costly to obtain.
• Complexity - Greater complexity means more logistics, more maintenance, and more planning. Rebreather divers must think ahead about absorbent, oxygen, service, spares, and travel support.

CCR requires an additional commitment of time, effort, and discipline as compared to sport diving. If you are not already an active and experienced diver, this may not be the right next step.

Rebreather Vocabulary

This section defines a few common terms used in rebreather diving. A rebreather does the following:

• Captures and recirculates the gas with a breathing loop.
• Removes carbon dioxide through a process called scrubbing.
• Maintains a breathable gas mixture by replacing consumed oxygen.
• Maintains loop volume during descent by adding inert diluent gas.

There are various rebreather designs and component layouts, but most recreational systems follow the same basic pattern. The loop uses counterlungs to store gas when you exhale and to supply gas when you inhale. A scrubber canister absorbs carbon dioxide, while the system maintains a constant oxygen level known as the PO2 set point.

Rebreathers manage this oxygen level in different ways. In manual systems (mCCR), the diver monitors oxygen sensors and adjusts oxygen manually. In electronic systems (eCCR), a controller continuously monitors the sensors and operates a solenoid valve to maintain the set point automatically. Hybrid systems (hCCR) combine a constant low-rate oxygen feed with electronic control to achieve the desired PPO2.

Rebreather diving is not simply a different set of equipment: it requires a different approach to planning, monitoring, and problem-solving. Many of the habits that work well in open-circuit diving do not translate directly to closed-circuit systems.

Prerequisites for CCR Training

The formal prerequisites for entry-level rebreather training are modest, but practical readiness requires more than just meeting minimum certification standards.

In the early days of formal recreational dive training, a rebreather certification was often viewed as the pinnacle of technical training, with extensive prerequisites and an almost overwhelming amount of information; some of it was of questionable value, and some of it was of questionable accuracy. Modern rebreather training standards spread content over a progression of courses that improves skills development and knowledge retention.

CCR accident analysis has improved the information content to focus more directly on safety, and recent research has dispelled some of the misleading conventional wisdom surrounding rebreathers. Today, the minimum formal prerequisite for entry-level certification is usually Nitrox certification, although I also recommend Deep and Rescue sport diving certifications. You should also have recent dive experience.

Rebreathers are revolutionizing technical diving, and many open-circuit technical divers are considering switching to CCR. However, overly rapid progression in CCR diving has been a factor in many accidents, and it is no longer possible to simply "crossover" the highest level certification from open-circuit technical diving directly to the closed-circuit equivalent. Modern rebreather training guidelines generally require the open-circuit technical training courses to be repeated in a slower progression of closed-circuit versions. Although guidelines allow entry-level rebreather training to include required decompression stops, best practice is for all divers who wish to perform such dives to first build some no-stop experience with their rebreather. If you are currently a sport diver who expects to progress into technical CCR diving, there is often no significant advantage to completing open-circuit technical training before rebreather training, depending on your goals and experience.

Highly experienced divers switching to CCR often face an additional challenge: they must overcome deeply ingrained open-circuit habits involving dive planning, equipment configuration, breathing patterns, buoyancy control, and gas management.

Rebreather Diving Safety

Rebreathers can be used safely, but they carry a higher risk profile than open-circuit scuba and require disciplined operation.

Statistics presented at Rebreather Forum 3 (RF3)¹ in 2012 suggested that closed-circuit diving carried substantially higher risk than open-circuit scuba in the available analyses. Some of that difference may reflect the fact that rebreathers enable more extreme dive profiles, which are themselves inherently higher risk than the dive profiles commonly attempted on open-circuit. At the time, many experts also believed that lack of experience, along with inadequate or poor-quality training, was a widespread problem in the rebreather community.

Subsequently, The Rebreather Education & Safety Association (RESA) and the Rebreather Training Council (RTC) were formed. These organizations are not training agencies; they are consortiums of rebreather manufacturers, dive training agencies, and knowledgeable individuals who have developed training expectations and standards intended to improve rebreather education. RESA published minimum training standards in 2018, and RTC now identifies ISO standards for rebreather diver training on its standards page. Even so, data presented at Rebreather Forum 4 (RF4)² in 2023 indicated that rebreather diving safety had not yet shown a clear statistical improvement over the preceding decade, reinforcing the importance of quality training and operational rigor.

No rebreather is foolproof, and the fact remains that compared with open-circuit scuba there is still a disproportionate number of rebreather fatalities, many of which have ultimately been attributed to diver error. Your safety while diving is controlled by you, not by your rebreather.

Choosing a Rebreather

Choosing your first rebreather is less about finding a “perfect” unit and more about selecting a suitable platform and instructor for your needs.

Because many open-circuit divers learned to dive on rental equipment, using a rental rebreather for the training course might seem like a viable option. However, rebreather training is unit-specific, and one of the major benefits of the course is that the instructor can optimize the rebreather for your individual needs, often including specific adjustments and customizations. There are exceptions where a rental unit is necessary, typically because the student's own rebreather is backordered or temporarily out of service. There are also occasional cases where someone wants the full educational experience of a rebreather training course but does not plan to own a rebreather or require certification. In these limited circumstances, temporary access to a rental unit for the duration of the course can be arranged. In most other situations, renting a rebreather for the training course is not recommended.

Buying your first rebreather is a classic chicken-or-the-egg problem, because prior open-circuit experience can be misleading and you will not yet have enough rebreather experience to make a perfect choice. There is no perfect rebreather; every model has strengths and weaknesses that make it more or less suitable for a given diver and mission. All major rebreather models are serious, capable units, and if your first rebreather comes from an established manufacturer, you are unlikely to make a bad choice.

For the TL;DR answer to this question: the Poseidon Se7en+ electronic CCR is my personal choice from among the many designs for which I have been certified. It is a well-proven design with good redundancy from an established manufacturer. It is also a uniquely automated design that is smaller, lighter, and simpler to use than many other rebreathers. The Poseidon Se7en+ is a robust eCCR choice for a wide range of sport and technical diving applications.

If you are uncertain about your selection, a carefully supervised "rebreather experience" may help narrow your choice, and I am happy to organize a private trial. However, please keep in mind that these experiences have limited value because closed-circuit diving has little in common with open-circuit diving. Imagine entering the water knowing nothing about open-circuit diving and with no buoyancy control skills, yet trying to decide which open-circuit equipment is "best" for your needs. Like automobiles, once you have selected a specific rebreather there are still several configuration options that determine the final unit delivered. I can help advise you on those choices, and Poseidon’s detailed FAQ will often answer many questions about specific models.

Perhaps the most important decision you will make is not the brand or configuration of your rebreather. The most critical decision is choosing a qualified instructor and training program.

Travel Logistics

Rebreather travel is manageable, but more effort than traveling with open-circuit equipment. Open-circuit divers typically travel with one dive bag plus ordinary luggage. With some compromises and selective use of carry-on baggage, many closed-circuit divers can also stay within that general model, but as a practical matter it can be difficult to remain within a single checked bag at 50 pounds. Staying within the 70-pound limit is usually possible, but two lighter dive bags are often far easier to manage. Either way, as a rebreather diver you should expect higher baggage fees than as an open-circuit diver.

Other logistics considerations include the availability of appropriately sized cylinders, oxygen fills, and carbon dioxide absorbent, commonly called sorb. The most difficult issue is often cylinders, especially valves. For remote destinations, some divers ship cylinders and absorbent ahead and then leave them behind, selling, trading, or donating them to the operator before departure. Even when the appropriate cylinders are known to be available at the destination, prudent divers often travel with a pair of specialized valves.

As rebreathers have become more popular, many destinations now have sufficient support infrastructure for manageable logistics with proper planning.

Cost of CCR Diving

Most divers should expect a total investment of approximately $15,000 to $20,000 to begin CCR diving. Here is how that usually breaks down: most major-brand eCCRs cost around $10,000, sometimes a little less and often more for fully optioned technical configurations.

To that you should add roughly another $1,000 to $2,000 in accessories, plus a starter package of consumables such as absorbent. Some open-circuit equipment you already own may be repurposed for closed-circuit use, such as bailout regulators, DSMBs and reels, masks, and fins, but often at least some of your existing equipment will not be suitable, which can add another $1,000 to $2,000. Training costs vary, but about $2,000 is typical, sometimes more depending on boat trip costs. If the training is not available locally, then add whatever travel and lodging you prefer, but assume an average of another $2,000 to $3,000. There are corners you can cut to reduce the initial cost, such as deferring technical options or buying refurbished equipment, but do not cut corners on the quality of the training.

The reality is that if a $15,000 to $20,000 budget gives you pause, then you should probably reconsider or delay the move to closed-circuit.

CCR Training and Certification Courses and Pricing

This progression outlines the typical path from entry-level CCR training and certification through advanced decompression training, with increasing depth, complexity, and responsibility. Rebreather training is conducted to meet training-agency-specific standards. I offer a rebreather training progression with multiple entry points, and each program has different prerequisites, information, skills, dive exposures, and limits. The programs are:

CCR Diver — Entry-level for sport divers

Entry point for open-circuit sport divers.

Divers learn to plan and conduct no-stop CCR dives within sport-diving limits. The emphasis in this program is on managing the rebreather and, should an issue develop, safely ending the dive on open-circuit bailout. Training time: approximately five days, including open-water training dives. Price for instruction and training materials is $2000.00; price does not include equipment rentals or boat trips.

Deco CCR 40M — Intro technical CCR

Entry point for open-circuit technical divers with at least 50 hours of experience, or CCR Divers with at least 30 hours of CCR experience.

Available in an air-diluent version, I prefer the Helitrox (21% oxygen, 35% helium) diluent version and teach divers to plan and conduct required-stop decompression CCR dives to a maximum depth of {150 fsw | 45 msw} using normoxic trimix diluent and a single off-board bailout cylinder. Using trimix diluent rather than air offers the benefits of reduced narcosis, better work of breathing, and improved scrubber performance. The emphasis in this program is on diagnosing and resolving in-water issues in order to remain on the rebreather loop whenever possible. Training time: approximately six to seven days including open-water training dives. Two of the training dives will be deeper than {100 fsw | 30 msw} with a planned decompression obligation. Price for instruction and training materials is $2500.00; price does not include CCR consumables, equipment rentals, or boat trips. This program content is sometimes referred to as "Mod 1 CCR".

Deco CCR 60M — Advanced decompression CCR

Qualifies the Decompression CCR Diver - 40M to independently plan and conduct multi-stop decompression dives to a maximum depth of {200 fsw | 60 msw} using trimix diluent along with two bailout cylinders and gases.

The diver also must have logged a minimum of 50 CCR dives and 50 CCR hours that include at least 20 dives and 25 hours on the specific unit, at least 20 CCR dives deeper than {100 fsw | 30 msw}, and at least 10 CCR required-stop decompression dives. The student candidate must complete a series of progressively deeper open-water multi-stop decompression training dives. Two of the training dives will be deeper than {160 fsw | 50 msw} with a planned decompression obligation. This program content is sometimes referred to as "Mod 2 CCR," but it is tailored to the candidate's prior training and experience; contact me to discuss your specific goals.

Deco CCR 100M — Deep trimix CCR

Qualifies the Decompression CCR Diver - 60M to dive to a maximum depth of {330 fsw | 100 msw} using very hypoxic trimix gases and three bailout cylinders.

The diver also must have logged a minimum of 100 CCR dives and 50 hours on the specific unit, including at least 25 CCR multi-stop decompression dives deeper than {130 fsw | 40 msw}. The student candidate must complete a series of progressively deeper open-water multi-stop decompression training dives. Other than an orientation dive within sport limits, all the training dives will be deeper than {130 fsw | 40 msw} with a planned decompression obligation, and two of those dives will be deeper than {230 fsw | 70 msw}. At this level, the required-stop training dives are typically conducted one per day. This program content is sometimes referred to as "Mod 3 CCR," but it is tailored to the candidate's prior training and experience; contact me to discuss your specific goals.

CCR Crossover — Experienced CCR divers switching units

These fast-paced programs are for the experienced and active CCR Diver who wishes to cross-train for certification on a different model rebreather.

Semi-closed-circuit divers and CCR Divers who have fewer than 10 logged CCR dives in the last 12 months must take a full CCR course instead of a crossover. This program is tailored to the candidate's prior training and experience; contact me to discuss your specific goals.

Prerequisites and content as described above will vary as appropriate to meet specific training-agency standards, but the programs have similar structure and elements: online programmed instruction review and/or assigned reading completed prior to arrival, facilities orientation, prerequisites and standards review, safety discussion, hands-on detailed assembly and configuration of the rebreather, classroom lectures, in-water equipment skills sessions, pre-dive trip briefings, rebreather setup using a checklist, half-day dive boat trips, open-water training dives, post-dive trip debriefings, and exit interview.

Class sizes are a maximum of four students and one CCR instructor, plus an in-water assistant when there are more than two students. I also provide additional education and learning opportunities whenever training-agency standards and logistics allow. The structure and expectations described above are consistent with the RESA Minimum Requirements³. You may wish to review that document to better understand what to expect from CCR training.

As with any scuba course, training is purchased, but certifications are earned only when the student and instructor both agree that the training requirements have been completed to their mutual satisfaction.

Contact Mark at CustomerCare@divegearexpress.com

If you are considering CCR training on the Poseidon platform, feel free to reach out.

Training with Mark

Training is conducted in Pompano Beach, Florida (South Florida), where conditions and logistics support a wide range of rebreather training scenarios. The logistics for rebreather diving are excellent. Water conditions are good year-round, and the range of local dives offers a useful mix of shallow and deep reef along with shallow and deep wreck sites for training. On-site training is also available; I have organized training aboard yachts and at resort destinations around the world.

Course openings are available most weeks of the year. Keep in mind that finishing on time assumes we will be able to dive without interruption from logistics or weather, and I recommend planning for an extra day or two. I typically begin classes at 9AM on a Saturday morning and suggest that travelling students plan departure for Sunday of the following weekend at the earliest. Many divers prefer a slower pace, and I am happy to accommodate that. Send me some date ranges that work for you and I will reply with specific availability options.

Travelling students may wish to stay at the Best Western Plus - Deerfield (4 stars on TripAdvisor), the Hilton Doubletree - Deerfield (4 stars on TripAdvisor), or the La Quinta Inn - Deerfield (3 stars on TripAdvisor) because they are conveniently located. There are clusters of chain hotels at the junctions of I-95 with Hillsboro Blvd and 10th Street. There are also many upscale private and chain hotels on the beaches in the area; the choice is entirely yours. You will also benefit from having a rental car during your stay, though ride-share services such as Uber or Lyft are workable.

There is a liability and assumption-of-risk waiver that you must read before class. There is also a medical form you must complete before class that contains questions about your health. If you answer "YES" to any of the questions, depending on the circumstances you may not be a suitable candidate for training or may be required to have a physician's evaluation clearing you for scuba diving activities. If you are currently a smoker, I require that you refrain from smoking for 24 hours prior to any in-water activities on the rebreather.

In preparation for the course, I ask you to read the following prior to attending the first day of class:

• Course-specific materials, typically printed manuals and/or online learning courses, as required by the training-agency standards.
• The manufacturer-supplied user manual for your specific rebreather model. The primary goal of reading before class is that you can identify major sub-assemblies, key components, and their functions, especially how to operate and interpret the electronics. Do not be concerned about the details of the checklists at this stage; you will review that material during class. The current version can be downloaded from the website of the manufacturer for your specific model.
• Rebreathers Simplified Revision 4 by Dr. Mel Clark. This text is recommended reading only for divers taking their first rebreather course. Although it is not a formal requirement of the training standard, it is very useful in providing a common vocabulary and also offers a strong review of basic physics and physiology as they apply to all rebreathers. This saves classroom time and allows that time to be spent gaining a deeper understanding of rebreathers.

Please arrive prepared: completing the assigned reading before class is important. Students who arrive unprepared often require additional time to complete the course and may be exposed to increased risk while learning critical skills.

Required Equipment

Rebreather diving is an equipment-intensive sport. Obviously, you will need your rebreather with BCD and harness. If you purchased your rebreather used, I recommend that it receive a factory-authorized overhaul prior to the course. Please be aware that training standards prohibit functional modifications to the rebreather unit that are not approved by the manufacturer. Other equipment you will need to bring includes the following:

• You will need a wet or semi-dry neoprene exposure suit, typically 3mil or 5mil in the summer and 5mil or 7mil in the winter, though you may also use a dry suit. A full hood, even if only nylon, and tropical-style dive gloves are recommended.
• You will need technical-style open-heel diving fins with boots. A spring or bungee heel strap design is strongly recommended.
• You will need a low-volume dive mask that fits well without frequent clearing. A key requirement is being able to clearly see the heads-up display mounted on your rebreather, which means the mask should provide a large downward field of view. If you have difficulty reading your gauges, you will need an appropriate vision-correcting mask with a bifocal lens.
• You will need a delayed surface marker buoy (DSMB) along with a safety reel and a line-cutting device.
• You will need a slate or other writing device. An executive slate or tablet style is best; an underwater notepad also works, but not a wrist slate. You will also need a surface alert device such as a Storm whistle or signal mirror.
• For off-board open-circuit bailout, you will need an open-circuit regulator with a 40-inch LP hose plus an SPG with a short HP hose or a button gauge. If your CCR supports standard quick-disconnect posts on the manual addition valves, a low-pressure BC inflator hose is also a good idea.
• For the advanced courses with planned required-stop decompression, you will also need a compact back-up mask, a back-up DSMB and spool/reel, and a back-up dive computer that offers a constant PO2 mode (aka CCR mode).
• Please bring your dive certification cards along with your dive log as well as a photo ID. You will not be able to dive until I can verify that your certification and the experience documented in your dive log meet the prerequisites required for training.

You'll also need the usual non-dive comfort items you are accustomed to using in tropical diving: swimsuit, towel, sunblock, sunglasses, and similar items. In the winter you will want a light jacket with a hood or a dive parka.