Connect with us

Equipment

The RB80 Semi-closed Rebreather: A Successful Exploration Tool

What rebreather has arguably logged the most exploration kilometers since its market introduction in 1998—an estimated 160 km plus (100 miles plus for you Imperialists)—and continues to rack up the klicks? It’s Halcyon’s RB80 passive-addition, semi-closed rebreather. Here WKPP greybeard and RB80 instructor trainer David Rhea reports on the RB80’s history, design & workings, training, and he offers the lowdown on its new sidemount progeny, the RBK. Looking for an electronics-free, sidemount bailout rebreather? Halcyon may just have your number.

Published

on

By David Rhea

Header image by David Rhea

Full Disclosure: Halcyon Dive Systems is a sponsor of InDepth.

In the early 1990s, the cave exploration conducted by the Woodville Karst Plains Project (WKPP) in the Woodville Karst Plains of Florida, especially Wakulla Springs, was becoming quite complicated. With dives averaging depths of 89 m/290 ft, with penetration being measured in miles, and decompression taking hours, it was becoming obvious that rebreathers would be necessary to move forward. In 1996/97, the WKPP began using a semi-closed circuit rebreather known as a Passive Variable Ratio-biased Addition Semiclosed Rebreather (PVR-BASR), nicknamed “The Fridge,” to extend their exploration and decompression obligations. This piece of equipment was a very large, bulky, and complex unit, and while it was uncomfortable above and below the water, the PVR managed to do what was intended and allowed for further exploration.

George Irvine and Anthony Rue with the Halcyon “Fridge” rebreather prepping for a WKPP dive. Photo from the GUE archives.

In 1996, a team of European explorers called the European Karst Plains Project (EKPP), who utilized the “Doing It Right” (DIR) techniques and philosophy of the WKPP, began using a semi-closed rebreather called the RB-2000. The unit was developed by the EKPP founder and director Dr. Reinhard Buchaly, who was inspired by the great success of French cave explorer Olivier Isler had at Doux de Coly and other cave systems using a custom made, triple redundant, semi-closed rebreather, the RI 2000 designed with the help of French engineer Alain Ronjat.

The RB-2000 unit was much smaller than the PVR-BASR, and utilized a very clever, intuitive, and reliable design. This design complemented the DIR philosophy used by both teams, and would become the choice for both groups moving forward.  By 1999, WKPP explorer Jarrod Jablonski and Robert Carmichael, the owners of Halcyon Dive Systems, worked out a deal with Buchaly to have Halcyon manufacture, sell, and service an American version known as the RB80.  

Designing a Semi-closed Rebreather

Being a cylindrical design 185 mm/7.28 in. in diameter, and 660 mm/25.98 in. tall —virtually identical to the size of an aluminum 80 cylinder—helped the RB80 get its name. The RB80 was designed to fit between the cylinders of a double tank configuration utilizing a specially designed frame, manifold, and switch block system. The economy of parts allows for maximum efficiency with only about 130 parts total. 

Images (L2R): The RB80 ready to rock, (R) Blake Wilson headed for the spring. Bottom: The RB80 dissembled. Note the countering bellows in foreground center right. Photos by David Rhea.

This design complemented the DIR philosophy of maintaining all of the diver’s back gas for emergencies, utilizing stage tanks for exploration and decompression. The gas switches utilized the same procedures taught by Global Underwater Explorers (GUE) but instead of swapping regulators from the mouth, the diver plugs a special QC6 swagelok fitted hose from the stage bottle into a switch block that feeds the gas into the rebreather. 

  • Subscribe for free
  • Area 9
  • Halcyon Sidemount

The stage bottle regulator is a standard open circuit (OC) configuration with the addition of one extra hose with a QC6 connector. The switchback also allows for a hose from the back gas to be plugged into the block in case of a stage failure or other emergency. 

Figure 1. Schematic of the RB80.
1. Dive/surface loop with non-return valves
2. Exhalation hose
3. Counterlung fore-chamber
4. Non-return valve to discharge bellows
5. Discharge bellows
6. Overpressure valve
7. Main counterlung bellows
8. Addition valve
9. Scrubber (axial flow)
10. Inhalation hose
11. Breathing gas storage cylinder
12. Cylinder valve
13. Regulator first stage
14. Submersible pressure gauge
15. Bailout demand valve

The vertical design of the RB80 has a very clever water removal tube that runs directly through the center of the scrubber bed and vents water along with a small volume of discharge gas. The unit is a passive addition semi-closed design, with no depth compensation and is tied to the diver’s respiratory rate. Roughly 1/10 of the respired volume of breathing gas is discharged into the water with each breathing cycle via the inner bellows and a familiar over pressure relief valve (OPV), commonly used on most dry suits. See Figure 2 and 3 below.

The RB80 utilizes a dual bellows counterlung system (versus traditional counter lungs), which reduces the loop volume each breathing cycle. When the loop volume is sufficiently reduced, it triggers the injectors made of components of an open circuit regulator that function quite similarly. Once the injectors fire, the loop volume is replenished with fresh gas. The unit has dual injectors for redundancy, which can be isolated at the switchblock if necessary.

The scrubber bed lies above the bellows in this vertical design and is manually filled by the diver before each dive. The scrubber is a 3.2 kg/7.05 lb design and will last approximately ten hours, based on more than twenty years of operational experience. Note that semi-closed rebreathers generally get longer duration on a scrubber given that a percentage of the breathed gas is expelled and replaced with fresh gas. 

The mouthpiece design incorporates a bail out valve (BOV) allowing the diver to switch from the rebreather to OC at the turn of a lever conveniently located in the center of the mouthpiece block. A hose routed from the right post regulator of the back gas is always live and gives gas immediately once the lever is turned. 

Assessing the Work of Breathing

New rebreather divers often state they feel the RB80 has a lot of breathing resistance. This is generally due to the fact that they are accustomed to modern OC second stages which deliver almost effortless on-demand breathing. Typically, modern second stages use VIVA (Ventura-Initiated Vacuum Assist) technology. This technology, along with the geometry of the second stage and the fact that the second stage is balanced, make for incredible light cracking effort. Upon inhalation, the initial cracking effort lowers the gas volume in the case, which pulls down the flexible diaphragm, activating the lever that opens the valve and allowing gas to flow to the diver. The VIVA then keeps the gas flowing at the same rate without the need for the diver to continue to draw on the regulator.  

By comparison with the RB80, the diver is simply pulling the gas through a one-way check valve, drawing the available gas in through the right inhalation hose, beyond the valve, into the mouthpiece block, and into the divers mouth. This entire system of gas flow does not have any boost effect like its OC sister and therefore feels as if you are working hard when, in fact, it is quite effortless. As a “virtually” closed loop, one simply draws the available gas through the inhalation hose into the diver’s mouth, and then exhales out a one-way valve at the mouthpiece, back through the left exhaust hose into the breather where the gas is scrubbed of CO2, water is removed, and the gas is replenished. 



Similar to OC, the rebreather does vary in breathing performance based on the diver’s position. If you have ever stood on your head diving OC, you feel a change in performance, as the second stage is much deeper than the lungs. The RB80 historically being a back mounted rebreather keeps the unit at a slightly shallower depth than the diver’s lungs, making inhalation slightly harder and exhalation slightly easier.  This difference is virtually indistinguishable; however, extreme head down or head up positions can seriously affect rebreather breathing efforts.  When worn in a side mount or stage position, the unit is in equal position with the lungs, making for very easy breathing. Fortunately, when a  diver is in near perfect trim, the RB80 performs best, as this is the ideal position for ease of breathing. 

Extending a Diver’s Breathing Gas

The RB80 is a serious gas extension device, providing 8-10 times the gas mileage of OC. By rebreathing one’s gas and only losing 1/10 of each breathing cycle into the environment, the RB80 can take a single aluminum 80 cf/11 ltr stage bottle and turn it into roughly 640 cf/18m3, or the equivalent of eight AL 80s. 

In cave exploration, we always start a project by setting up the cave with “safeties.” These are caches consisting of two bottles each equipped with a stage regulator complete with an OC second stage as well as a QC6 equipped drive hose to plug into the RB80, and a submersible pressure gauge (SPG). These bottles are placed roughly every 3,000-5,000 ft/900-1,500 m in the cave, and will remain there throughout the exploration. The safeties are checked by support divers prior to every push to ensure function and adequate gas volume. The bottles are properly filled and marked with the proper Maximum Operating Depth (MOD) gas for the dive, and they are labeled “SAFETY.” 

With rebreather diving, it is paramount that adequate bailout gas be available in case of a single point failure on the rebreather. Rebreathers, while quite robust, have many single failure points, i.e., the breathing hoses, one way valves, OPV, the bellows in the case of the RB80, and even the diver’s mouthpiece. As mentioned, the injectors have redundancy and can be isolated in case of issues, and a spare mouthpiece is always carried by the diver in case of a serious tear or damage. 

Any other single point failure could render the rebreather inoperable, forcing the diver to return and complete all decompression on OC, demanding eight times the amount of gas that had been used at this point in the dive. So, in addition to 100% of the back gas being maintained for bailout, cave exploration demands the discipline of staging the cave with safety bottles, safety scooters, as well caches of decompression gas, and proper support personnel.

RB80 vs. an Electronic-controlled Closed Circuit Rebreather (eCCR)

A variety of eCCRs are available by manufacturers. These units are extremely efficient, as no gas is lost from the breathing loop. The eCCR can be 25-50 times more efficient than OC. However, in addition to the single point failures listed above, which are common on all types of RBs, the eCCR, has additional concerns that prevent it from being a consideration for many cave exploration groups like the WKPP and GUE-affiliated El Centro Investigador del Sistema Acuífero de Quintana Roo (CINDAQ) foundation, which hosts the  Mexico Cave Exploration Project (MCEP) in the Yucatan. 

Most eCCRs have three oxygen sensor cells that must be meticulously maintained and work together with a solenoid and an electronic controller, using a concept called voting logic. Together with an oxygen bottle and a diluent bottle, the eCCR mixes the diver’s gas during the dive within a (PO2) set point range that is predetermined by the divers. By having three oxygen cells, the controller will side with the two that have the most similar reading if one were to start to read differently from the other two. 

Lauren Fanning and Blake Wilson diving their RB80s at Emerald Sink, FL. Photo by Kirill Egorov.

Unfortunately, voting logic is inferior to the gold standard—triple redundancy: main unit, back up, back up for the back up—and has been known to be incorrect i.e., in the case of a double cell failure. Discipline, and pre- and post-dive maintenance, are the key to maintaining good sensor reliability.

When diving an eCCR, it is necessary for the diver to constantly monitor the gas mix in their loop in order to ensure that they safely avoid hypoxia or hyperoxia. For an easy-to-see reminder that the unit is working within the safe limits set by the diver, most eCCRs rely on a heads-up display (HUD)— generally mounted to the inhalation hose—that shows a small series of lights indicating green for good, yellow for caution, and red for danger, in case the PO2 in the breathing loop is getting out of range. This is of course driven by a controller that gives real time PO2 that can be viewed on the diver’s handset. Most eCCRs provide at least one handset as well as the HUD to ensure proper redundancy.  

One of the reasons many cave exploration groups like the WKPP strictly use the RB80 is its simplistic mechanical, reliable design. With the RB80, the gas is premixed into the stage bottles, and the back gas is always mixed for the MOD of the max depth expected to be reached during the dive. With the RB80, there is no gas mixing during the dive; the gas is plugged into the switch block similar to doing an open circuit gas switch. The gas is filled, properly analyzed, and the content label is attached to the neck of the bottle prior to leaving the dive center. 

The bottles all have properly placed MOD stickers on two sides of the bottle for easy identification by both the diver and his team mates, plus a MOD sticker placed on the bottom of the cylinder that can be identified by teammates when being viewed from behind. In the water, the proper stage bottle is selected for the MOD, and the gas is safely plugged in at the proper switch depth, but only after the bottle has been properly identified, verified by the buddy, and the drive hose confirmed with the bottle that has been chosen, similar to open circuit gas switches. 

WKPP explorer David Doolette measuring a mastodon bone in Wakulla Springs B Tunnel. Dr. John Rose in background. Photo by David Rhea

The most dangerous thing about the RB80 (and semi-closed units in general), is the oxygen drop, especially in shallow water [See the Loop Gas calculations section of the RB80 page in Wikipedia]. Due to the fact that oxygen is being consumed during respiration, and gas is discharged from the inner bellows with each exhalation, the oxygen drops slightly with each breathing cycle until fresh gas is replenished from the injectors, typically every two to four breaths. For this reason, one must be cautious when using the RB80 at shallow depths (when the ambient pressure is low) or when using mixes with a lower oxygen fraction as a travel gas. 

The drop in oxygen levels also means there is a slight increase in inert gas that remains in the loop and that needs to be taken into consideration for decompression. Both of these nuances of the RB80 are easy to calculate and adjust for prior to the dive. 

During RB80 training, both the oxygen drop and the increase in inert gas load are addressed and easily able to be factored in. The theory is discussed in an RB80 class, and software is available to easily do quick calculations.  All of this can then be programmed into GUE’s Buhlmann-based desktop decompression program, DecoPlanner, for proper dive planning.  Like most rebreathers, the RB80 has additional complexities requiring proper pre-dive assembly, testing, maintenance, and post-dive discipline. 

Training on the RB80

The WKPP was established in 1995, and from the beginning, adopted a standardized approach to gear configuration and procedures. Initially, this approach was called “Hogarthian,” after early WKPP pioneer Bill Hogarth Main. Later, project director George Irvine added to the standardization and coined the phrase “Doing It Right,” or DIR, to represent this standardized approach.  In 1998, Jarrod Jablonski founded GUE, which offered exploration-based training utilizing WKPP’s standardized approach and gear configuration. Once Halcyon started building the RB80, GUE began offering formal training. Currently they are the only training agency to do so. 

From the beginning, GUE’s RB80 training has been exploration-based, with a heavy emphasis on failure-based training i.e. dealing with equipment failures as a team, similar to other GUE courses. Exploration-level cave diving has complex exposures that require divers to return from deep inside the cave, and then make a vertical ascent to return to the surface. With the addition of the RB80, divers are able to extend their penetrations exponentially, adding as much as 12-14 hours of decompression on some dives alone. Conventional rebreather training does not properly prepare someone for these types of exposures. 

RB80 Divers on the wreck of the freighter Judge Hart in Rossport, Canada. Photo by David Rhea

GUE divers have historically been required to take Fundamentals, Tech 1, and Tech 2 with a minimum of 25 dives at each level between classes prior to beginning their RB80 training. This is in addition to the Cave 1 and 2 level training and experience required to begin cave exploration.  The investment of time, energy, and resources necessary to become a GUE/WKPP exploration cave diver makes for a very serious explorer who has the skills and experience necessary to conduct dives with this level of exposure. The failure-based training also builds the diver’s confidence, repetitive learning, and instincts necessary to safely explore. 

One of the many reasons for the long term success of the RB80 has been this extremely regimented training by GUE’s four active RB80 instructors. In addition to the most intense and demanding rebreather training available, GUE RB80 students must purchase the unit prior to taking the training. This alone narrows the attendance to only the most serious explorer, as no rental option is considered. 

  • Subscribe for free
  • Area 9
  • Halcyon Sidemount

Until fairly recently, GUE divers were the only ones using the RB80. Even then, only those willing to take the robust training who had an exploration mindset learned to dive the unit. Currently there are 150-200 GUE divers certified to dive the RB80. The discipline and attitude of these explorers has ensured that the RB80 has been responsible for more kilometers/miles of cave exploration than any other rebreather in the world. I estimate that more than 161.6 km/100 mi of cave passage has been explored using the RB80. 

The discipline and attitude of these explorers has ensured that the RB80 has been responsible for more kilometers/miles of cave exploration than any other rebreather in the world. I estimate that more than 161.6 km/100 mi of cave passage has been explored using the RB80.

A Specialized Exploration Tool

For 30 years the WKPP has been mapping the underwater labyrinth of the Woodville Karst Plain, having mapped over 56,609 m/185,000 ft of cave passage with more than 35,189 m/115,000 ft below 58 m/190 ft. The RB80 has been one of the most vital keys to this success, including the world record dives in Wakulla and the following traverse. It is the only rebreather used for exploration on Woodville Karst Plain projects. Presently, virtually all exploration being conducted by the WKPP below 61 m/200 ft is exclusively done on the RB80. 

WKPP dives in Florida on the RB80. Photo by David Rhea.

Over the years, and especially during the Wakulla exploration heydays, one of the growing concerns was running out of scrubber material during the dive. On the biggest dives, the entire RB80 double tank configuration would be swapped at the deep portions of the decompression for a fresh ‘breather with smaller double five-liter bottles and fresh scrubber material. Note: an advantage of the RB80 over an eCCR is that the valves can be closed and the unit reliably stored underwater like a stage bottle for bailout.  It can then be quickly turned on and dived.

In 2008, CINDAQ’s MCEP project also adopted the RB80 and has done countless hours of exploration in the caves of the Yucatán. Between January 2018 and December 2020, for example, MCEP exploration divers mapped in excess of 180,000 m/594,000 ft of new cave passage in Ox Bel Ha alone using RB80 technology. 

As CINDAQ board member and co-owner of Zero Gravity Dive Center, Christophe Le Maillot, explained, “It is such a sturdy and intuitive unit. In all the years we used it, we have never had to terminate or cancel a dive because of a malfunction. It’s a real work horse!” Like their sister WKPP team, the MCEP exclusively uses GUE-trained RB80 divers for their exploration dives. 

GUE divers have also utilized the RB80 for cave exploration projects in China, the Nullarbor caves in Australia, caves in the south of France, cave and wrecks of Italy including the Pantelleria project, the Alviela cave project in Spain, and other karst areas around the world. In addition to cave exploration, the RB80 has been utilized by GUE divers on the west coast for the ghost net removal, and by GUE wreck divers in Canada and around the world. 

Introducing the RBK, a Sidemount RB80

In response to explorers wanting a stageable version of the RB80 as both a travel and/or bailout rebreather, Halcyon began working to develop a modified sidemount version of the RB80, called the RBK. The first version was called the RBK1 and after several years of modifications Halcyon produced two more revisions, the RBK 2 and the RBK 3, referred to simply as the RBK.

Halcyon COO Mark Messersmith diving the RBK in Mexico. Photo by Sam Meacham.
Sam Meecham with a pair of RBKs. Photo courtesy of CINDAQ.

The overall diameter of the RBK is the same as the RB80, but by reducing the height of each section, the overall length of the unit has been reduced to 50 cm.  Though the scrubber was reduced in volume to 2.4 kg/5.29 lb, the scrubber duration is rated for approximately eight hours based on user experience [See InDepth’s Rebreather Holiday Shopping Guide for add’l spec details]. Because of the smaller form factor, the RBK offers a 6-8:1 gas extension versus 8-10:1 on the full RB80.

The sidemount RBK has been used as a sidemount, travel, and bailout rebreather by both the WKPP and the MCEP, which has been testing and helping to refine various RBK prototypes since 2015. On recent long-range explorations through small passages, the RBK has proven to be an outstanding tool for shallower, long distance cave exploration. MCEP instructors are now working with the GUE board of directors and other RB80 instructors to develop a RBK sidemount training course, which should be available in the not-too-distant future.    

New Non-GUE Users

Andy Pitkin with a sidemounted RBK bailout rebreather. Photo by Kirill Egorov.

Over the last few years, Halcyon has made the RBK available to select non-GUE divers. They have sold custom versions of the RBK to militaries around the world. In addition, they have provided RBK units to exploration divers from Karst Underwater Research (KUR), who have been using the RB80 as a side mounted bailout breather for their recent long range exploration dives at Weeki Wachee Springs and other systems. The divers received their RBK training directly from Halcyon. 

As KUR project director Andy Pitkin put it, “It is undeniably true that ‘simplicity is the ultimate sophistication,’ as Leonardo Da Vinci once noted. The RBK has proved itself to be close to a perfect tool for our particular application, far exceeding my initial reserved expectations.“  

From its conception, it was quickly obvious that the RB80 would be around for a very long time. The simplicity, safety, and the robust mechanical nature of the unit, combined with rigorous training, and highly experienced users, arguably make RB80 and RBK the ultimate exploration tools.

Subscribe for the InDepth Newsletter

Dive Deeper:

InDepth’s Rebreather Holiday Shopping Guide (2020)

Halcyon: Using The RB80 As A Sidemounted Bailout Rebreather by Andy Pitkin, Karst Underwater Research (2018)

GUE: DOUX DE COLY: GUE Expedition with RB80 (2004)

Introducing the RB80 by Michael Waldbrenner and Dr. Reinhard Buchaly 

Deep Tech: Victory At Last (1998): Olivier Isler is setting penetration records with a triple-redundant semi-closed rebreather

RB80 Series on GUE.tv


David Rhea is an active GUE instructor and instructor evaluator, having been with GUE since the earliest days. An avid explorer with the WKPP since 1998, David has explored caves in China, Florida, Australia, Mexico, and France. A passion for diving started at age six, leading David to make his first dives at age nine. He became a scuba instructor at age 18. David has worked full time in the scuba industry for over 40 years, and has worked for Scubapro since 1995. David is as passionate today about exploration, teaching, and underwater photography and managing his Florida Scubapro territory as he has ever been. 

Equipment

InDEPTH’s Holiday Rebreather Guide 2023

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

Published

on

By

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

A Guide to Backmount, Sidemount and Frontmount Rebreathers

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

Remember you can find all of the Rebreather Forum 4 presentations here on GUE.tv: REBREATHER FORUM 4

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

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

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

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

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

Buddy Inspiration advertisement from 1998. Courtesy of AP Diving.

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

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

Your Geeky Holiday Guide

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

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

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

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

It’s The Concept, Stupid

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

  • Area 9

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

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

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

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

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

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

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

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

Backmount Rebreathers

* In 2005, AP Diving launched its Vision electronics with In-Plane Switching (IPS) which enhances colour and visibility
**Typical scrubber duration using AP Tempstik increases practical duration to more than double CE test rate figures – as the AP Tempstik shows scrubber life based on actual work rate, water temperature and depth.
*** The work of breathing is the effort required to push gas around the breathing circuit BUT that figure alone is meaningless without knowing two other parameters: Hydrostatic load and elastance. Note that AP Diving rebreathers meet the CE requirements in all diver attitudes for both Hydrostatic Imbalance 0 degrees (horizontal, face down) and Hydrostatic Imbalance +90 degrees (vertical, head up.)
**** APD’s handset offers a “dual display” feature showing data from both controllers on the same handset. The user can also see the gradient factors chosen and the mVolt outputs of the cells by holding a button down.
* Divesoft will offer an upgrade for existing Liberty users
* Note that we plan to re-release our “Intervention CCR” (iCCR) in 2021. The unit was withheld due risk of loop being force dived when unsafe (pending re-release 2021).This enables the diver the option to manually trigger bailout to a known safe OC gas at any time with one finger and/or auto-bailout the diver if loop gas being breathed reaches unsafe level. Either Hi/Lo PPO2 or high End-Tidal CO2.
**For CE certification the recommended Apocalypse Type IV CCR scrubber duration is 2hr 45min to a maximum dive profile surface to surface of 100m in 4’C water to 2.0% SEV (20mb) at the mouth.
***iCCR (2009) 3x digital galvanic coax, iCCR (2021) x2 galvanic 1x solid state
****All performance data near near identical to single scrubber option other than increased scrubber duration of up to 5 hrs to 100 m profile in 4’C water)
Published Testing: https://www.opensafetyglobal.com/Safety_files/DV_OR_ScrubberEndurance_Retest_SRB_101215 .pdf https://www.opensafetyglobal.com/Safety_files/DV_OR_WOB_Respiratory_C1_101111.pdf https://www.opensafetyglobal.com/Safety_files/DV_DLOR_HydroImbal_101116.pdf
(FMECA) https://www.deeplife.co.uk/or_fmeca.php
* CisLunar series, MKVI 2009, SE7EN 2013, SE7EN+ 2019
** 40 m coldwater EN14143
*** Backmounted Trimix 10/70, 40M test: Backmounted Air
**** SE7EN+ Sport EU incl (harness, wing, computer, cylinders and sensors)
  • Halcyon Sidemount

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


 

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

Sidemount Rebreathers

*Pre 2021 units are upgradebale
* For a tour of KISS rebreathers see: https://www.youtube.com/watch?v=lelpTfGSYeE
https://www.facebook.com/T-REB-678683672151944/

Frontmount Rebreathers

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

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

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

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

Continue Reading

Trending

WordPress PopUp Plugin