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Keep It Simple Sidewinder

This month, we continue to explore innovative rebreathers on today’s market with a dive into KISS’s split-canister designed mCCR, the Sidewinder, launched in 2016. Designed to address some of the specific challenges of sidemount rebreathers, the Sidewinder has gained a passionate following among cave divers and explorers, as tech instructors Jake Bulman and Skanda Coffield explain.

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By Jake Bulman and Skanda Coffield. Header image: Skanda decompressing in “Cenote The Void”, a deep cave currently under exploration by the team. Photos by Alvaro Herrero at: @mekanphotography unless noted. Full disclosure: Protec Dive Centers owner Patrick Widmann is the KISS Training Director.

Since 1998, KISS Rebreathers has been designing and producing rebreathers known for their simplicity, reliability, and field serviceability. The KISS Classic, designed by the original owner Gordon Smith, has been used by explorers around the world for more than two decades. The Orca Spirit is a lighter back-mounted option from the KISS Classic, and features scrubber design that would later be carried over to the Sidewinder. As the need for a sidemount CCR grew and grew, KISS released the Sidekick. Surrounded by a hard metal shell, this was specifically made for harsh environments. Due to being an independant, self contained unit it could easily be donned/doffed at the surface or underwater, pushed through restrictions, or worn as a bailout rebreather (BOB).

One of our more well-loved units around Protec Dive Center

The Sidewinder is unique in that instead of being designed to meet the needs of a specific environment or dive type, fulfilling a specific person’s needs was the goal. Josh Hotaling, a Marine Corporal who lost both his legs in combat, wanted to start using rebreathers for his dives, but the available sidemount rebreathers had changes of balance throughout the breathing cycle due to the counterlung being on one side of the diver. Mike Young, with input from Edd Sorenson, worked on developing a unit that would be balanced while still being light, small and reliable. In 2016, the Sidewinder was born.

Left to right: Jake, Skanda, and Danny (student), during the final day of his Air Diluent class.

Our first real exposure to the Sidewinder came after Phillip Lehman of the Dominican Republic Speleological Society bought one and trained with Edd Sorenson in Florida. Between the two of us, we had previously owned, dove or been instructors on several units, including JJs, Sidekicks and Pelagians. While all of them have some nice features, they also have their downsides. Either they were very heavy, making buoyancy significantly more difficult (particularly in the shallow caves of Mexico), too large for the size of the caves we aimed to explore, or suffered from other issues. Small restrictions, cenote entrances that are difficult or impossible in backmount, and logistics of reaching some of the cenotes in the first place, meant we needed a sidemount rebreather.

Sidemounted CCRs in a Pre-Sidewinder World

At the time, sidemount rebreathers had two principal drawbacks: While each unit has taken a different approach, and sometimes solved one, a solution to both that doesn’t introduce new problems has proven difficult.

First of all, these rebreathers replace one of the sidemount tanks, giving divers the vertical profile of a standard sidemount configuration while they carry one bailout tank (which serves as diluent for most of them as well). This not only causes redundancy problems in the case of equipment failure on that tank, but also bail out range problems. Many people move to a rebreather to do bigger dives than they can on open circuit, and one bailout tank does not get you very far. Additional bailout tanks can be worn as stages, but this creates a larger vertical profile, significantly diminishing one of the main benefits of sidemount rebreathers. Stages can of course be removed, pushed through restrictions and put on again but it adds significant time and effort to passing through each restriction.

The second major drawback of sidemounted rebreathers has to do with the movement of gas during the breathing cycle. When divers exhale, the gas moves into the counterlung which is inside the rebreather on either the left or right side of the diver. This creates a shift in lateral trim that, while manageable, undoubtedly adds some level of task loading, even if it is subconscious.

Skanda swimming through one of many lower sections of the area

On the Sidewinder, unlike other sidemounted units, the scrubber is split into two canisters that allows them to sit alongside divers’ bodies, on top of the two standard sidemount tanks. Problem one, bailout placement and redundancy, solved. In this position, the canisters  slightly add to a diver’s profile, but it is hardly noticeable. In fact, in many photos it can even be hard to see that a diver is wearing a rebreather at all, with only the loop giving it away. 

Having two scrubber canisters also provides a level of redundancy regarding CO2 management. Scrubbers, designed to “scrub” the CO2 from the gas, can allow CO2 to pass through them for various reasons including packing errors, water, or overuse. Having two helps to reduce the likelihood of most causes of excess CO2.

The counterlung, which sits on the divers back and connects the two absorbent canisters, is the next critical piece to the puzzle. By being so close to the position of the diver’s lungs, the change in trim throughout the breathing cycle is negligible. This difference cannot be overstated enough. Regardless of how comfortable one becomes with the shifting of gas on other side-mounted rebreathers, it will always use some level of attention and energy to compensate for that shift. This is most clearly noticed in the performance of entry-level rebreather divers. Problem two, lateral trim, solved.

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The List Goes On

The Sidewinder is one of the lightest rebreathers on the market. [Ed. The Sidewinder is 12.3kg/27.1 lbs., which is lighter than the Liberty SM 22kg/48.5 lbs., but heavier than the RBK 8.62 kg/19 lbs., which is the lightest on the market] This can be a real consideration for divers with back or shoulder injuries, or who need to transport the unit long distances, across difficult terrain or through dry caves. Like open circuit (OC) sidemount, the tanks can also be carried to the water separately. The rebreather can be carried in a single bag, whether for jungle hiking or taking your carry-on luggage during air travel making it very nice to travel internationally with! 

Once in the water, the other advantage of a lightweight rebreather becomes apparent. The heavier the unit, the more gas is required to offset that weight. Sometimes this can be done with thicker undergarments or lighter tanks, but this is not always possible. When changing depths, managing buoyancy requires constant adjustments due to the compression or expansion of gas. With lots of gas between the three gas spaces (wing, dry suit, and CCR) the change in buoyancy happens very quickly. 

The Sidewinder is incredibly comfortable and easy to dive because of the drastically reduced gas needed to offset the weight. This gives the diver more time to react before the ascent/descent speed starts to pick up. With buoyancy not being a constant struggle to maintain (especially in shallow and constantly changing cave profiles),  divers are able to devote more of their focus to monitoring themselves, their team and their surroundings, allowing for greater awareness.

The Sidewinder is a mechanical rebreather, meaning that the oxygen is added via a constant mass flow orifice rather than an electronically controlled solenoid. Constant mass flow works via a combination of a small orifice and a fixed IP (internal pressure) first stage. Unlike a normal first stage that compensates for depth by increasing the IP during descent, the fixed IP first stage remains constant regardless of depth.

 If a diver descends to the depth where ambient pressure is equal to that of the first stage, the flow stops, and the manual add button will not add anything. This creates a depth limit, usually 80-90 m/260-300 ft. The flow of oxygen at shallower depths is matched to the amount metabolized by the diver, which maintains the PO2 in the loop, and makes buoyancy much easier. This shifts more control of the rebreather to the diver and removes potential failure points when compared with electronic rebreathers (eCCR) which use a solenoid to automatically add oxygen, when needed to maintain PO2.

Solenoids can be frustrating due to unfortunately timed injections changing a diver’s buoyancy; hence many technical divers will opt to run the rebreather manually to avoid this. Manually running a rebreather requires practice, and increases task loading. That being said, electronic rebreathers do have a place, and several reliable, proven machines exist on the market. This is a personal choice.

The Sidewinder handles water quite well. While water cannot be removed from the unit while diving, it continues working even with substantial water inside. Not only does the diver have two canisters, but the counterlung lies between them and acts as a water trap. It is not uncommon to find water in the bottom of a counterlung if they had water ingress, but the inhalation canister will be dry except in the worst of floods.

If absorbent is fully flooded, there will not be enough contact with the gas to react with it and remove the CO2. However if the sorb gets wet, then water is allowed to move out of the canister, and the sorb will continue working to a certain extent.

Skanda surveying a newly explored section of cave

Who is Using the Sidewinder and Why?

Historically, rebreathers were used by people who needed them for a given complex dive or lengthy project, in spite of the extra cost, serviceability, hassle, bulkiness, difficulty, and risks involved. If rebreathers were not needed, they were not used. The Sidewinder was not much different in this regard, with almost all of the early users being cave divers or explorers. However, as many of these barriers have been either removed or reduced, many divers have begun using them, not because they need to, but because they want to.

Cost: Sidemounted rebreathers are generally smaller, and in the case of KISS units, do not feature expensive electronics. This has brought cost to nearly half of what some of the mainstream back-mounted units cost, making it feasible for a much larger audience.

Serviceability: Just like open circuit regulators, rebreathers do require maintenance and servicing. In general, more complex and complicated equipment is more difficult to service yourself , should you even want to. Many eCCRs require that the electronics be sent to the factory or authorised service centre if repairs are needed. The Sidewinder is incredibly simple, it has few parts, and it does not require specialised tools to service (except the orifice tool). The servicing of the unit involves replacing o-rings and not much else! This is great for divers who want to service their own gear or who live far away from someone who services technical dive equipment. Also, during remote expeditions, the rebreather can be serviced without time delays.

Hassle: Setup and breakdown of the Sidewinder is quick and easy, requiring as little as 10 minutes each way for experienced users. It does not require altering your sidemount setup, grabbing different tanks, or accessing a bench in order to put one on. For people who do not need it, this goes a long way towards making it something they want to do.

Bulkiness: Larger rebreathers are often wider than some of the smaller framed divers, and nearly as heavy. Nobody likes carrying heavy equipment around, so the lighter it is, the better. We often find ourselves talking with other divers in the parking lot while in our suits and rebreathers which would definitely not happen with heavier equipment.

Difficulty: From setup to disassembly, and all the diving in between, the sidewinder is extremely comfortable and easy to use. This only gets more pronounced as you put more time into it. The days of first time rebreather tryouts being a difficult, frustrating experience are behind us, and it will only get easier.

Risks: Rebreathers will always come with risks, and that does not change between units. In the past, people accepted the risks because risk was required for  their particular dives; however, accepting the risks because one wants to dive is perfectly valid as well. As long as the risks are fully understood—which can only be managed through high quality training—each diver can make their own decision.  The vast majority of risks taken in life are for things we want to do, not that we need to do. 

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Due to these differences, divers of all backgrounds are dipping their toes into rebreather diving, with many deciding it’s something they want to do after they try it. For anyone who previously thought CCR diving took too much time and cost too much money—for instance, people who struggled to carry heavier units, divers wanting to have close encounters with marine life, photographers needing the time to shoot their perfect image without bubbles, instructors without a lot of time to set up their units, or divers on vacation wanting to spend it relaxing—rebreathers are suddenly not only feasible, but desirable.

That being said, there is still a community of hardcore cave explorers utiliizing the Sidewinder. People have experimented with using one in a dual-ccr setup; although, to our knowledge, this has not been put into practice yet in any significant way. A Sidewinder does fit the bill for that purpose however, and can be easily fit with a back mounted unit or a “tube style” sidemount rebreather. We imagine in the coming years we will see this on some of the bigger projects around the world.

How Our Diving has Changed

Our team has been using rebreathers for exploration for quite some time now. But we would never have gone through the effort of using one unless necessary. That was mainly because it took more time to set up and breakdown, was less comfortable, required more equipment, and limited where we could access compared to sidemount OC. The idea of the rebreather being the rule instead of the exception was unimaginable, especially considering a majority of the diving here in Mexico is shallow.

Yet, you will almost always find us diving the rebreather regardless of what we are doing. It no longer takes extra time, adds difficulty to the dive or runs the risk of expensive repair costs. It feels natural. And makes dives more fun!

No longer are we tourists in an alien environment relying on equipment that shifts our balance each time we take a breath. Nor do we need to sacrifice comfort and freedom of movement to extend our limits. With the Sidewinder, we feel like locals, completely adapted to the environment around us and free to move about as we like. The limiting factor is now the diver, not the equipment.

Jake floating in the shallows after practicing skills with newly certified sidewinder divers

The Sidewinder has Changed Our Game

The Sidewinder is incredibly easy to use. It not only creates an enjoyable experience, but contributes to safety. The level of awareness, understanding of the unit, control and stability that can be seen in entry level divers is shocking. After a few minutes of swimming around in a tryout, first time CCR divers could often be mistaken for highly experienced rebreather divers based on their buoyancy and control in the water. The simplicity of the unit regarding design and “diveability” has allowed us to spend more time training people to be safe, competent divers who truly understand their rebreathers, as well as the risks that come with them and how to manage those risks..

Training aside, it has also changed the game when it comes to exploration in caves around the world, which has led to some truly epic discoveries, but that is a story for another day!

Dive Deeper

Sidemount Pros: KISS Sidewinder 100 Hours In

Website: KISS Rebreathers

InDEPTH: My Journey Into Sidemount Rebreathers by Becky Kagan Schott


Originally from Canada, Jake Bulman is a full-time cave diving and CCR instructor at Protec Dive Centers in Mexico. The last several years of teaching have been almost exclusively sidewinder focused, from try dives to CCR Cave classes, 4C to 24C, and in several countries around the world. Outside of work, he can be found on exploration projects in local caves of a wide range of depths, distances, and sizes.

Since 2016 Skanda Coffield has been living in Mexico, working at ProTec Dive Centers. Originally from Australia, he made the move to be close to the longest underwater cave systems in the world. When not teaching cave diving or training new sidewinder divers, he spends his time diving his Sidewinder and exploring new and old cave systems.

Equipment

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!

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InDepth’s Holiday Rebreather Guide: 2022 Update

by Michael Menduno, Amanda White and Kenzie Potter

Holiday images by Jason Brown, BARDO CREATIVE

A Guide to Backmount, Sidemount and Frontmount Rebreathers

1DEC 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!

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: 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)

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.

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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 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.

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