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Bringing Breathers To Antarctica

Thinking about bringing your rebreather on one of Faith Ortins’ Blue Green Expeditions to the Antarctic? What makes you think it will work? John Heine, Diving Safety Officer for the U.S. Antarctic Scientific Program, sought to answer that very question. What he found may surprise you. Just the cold facts, ma’am!

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By Michael Menduno, original paper by Dr. John Heine

Do rebreathers work in ice-cold water, and even colder air at the surface? Those are the questions that research scientist at Jacksonville University Marine Research Institute and veteran diver John Heine sought to answer in a 2016 study funded by the National Science Foundation (NSF), which oversees the U.S. Antarctic Program (USAP), including scientific diving.

“We had an increasing number of queries from researchers that wanted to use rebreathers in the Antarctic,” Heine, who is the Diving Safety Officer for USAP and a member of its Diving Control Board, explained. “The problem is we couldn’t answer the [fundamental] question: will they work or would it be too risky? So, we decided to evaluate a number of rebreathers to see how they performed.” The results of the study were published last year (see foot note 1).

Scientific divers, who operate under an exemption from the Occupational Safety and Health Administration’s (OSHA) commercial diving regulations, have been diving in Antarctica since the 1960s. However, the exemption requires that diving operations be approved by the relevant institution’s Diving Control Board (DCB), in this case USAP’s, which has limited diving to open-circuit scuba. Though there have been a few non-scientific rebreather operations conducted in Antarctica, including the Wes Skiles 2002 Ice Island Project with explorer Jill Heinerth, and a Disney wildlife filming expedition on the Peninsula, these have been poorly documented.

Photo courtesy of Dr. John Heine.

The performance of open-circuit scuba equipment in freezing water is well known. Relevant equipment is regularly tested by the U.S. Navy’s Experimental Diving Unit (NEDU) and within the USAP, and certain regulators, such as the Sherwood Maximus, that perform well in icy conditions, have been approved for use by scientific divers.

Not so for rebreather technology. NEDU presumably has extensive knowledge of the use of rebreathers in cold water—it’s known that Navy Special Forces divers lock out of submarines in arctic waters. However, according to Heine, they won’t(or are unable to) discuss their experience or share data. In fact, as I learned when I did a profile of the NEDU for Alert Diver magazine a few years ago, they don’t even like to acknowledge that sailors dive from submarines.

Putting Rebreathers To The Test

Due to their silence, lack of bubbles, and extended range, an increasing number of scientists have employed rebreathers in their research, albeit in warmer waters, over the last two decades. Not surprising, there are also numerous potential scientific applications for rebreathers in the frigid depths of Antarctica.

These include wildlife behavioral studies, under-ice collections and sampling, and use in the McMurdo Dry Valley lakes to minimize mixing of water layers and adding exhaled gases into the environment. There are also the potential benefits of extending divers’ time and depth underwater, and of course breathing warm, recycled gas as compared to open-circuit scuba.

However, there were many unknowns. Rebreathers are typically tested at temperatures down to 39.2° F /4° C for CE certification. But that’s a big difference with the sub-freezing 28.6° F /-1.8° C water temperatures found in Antarctica, where air temperatures typically average -20° F/-29° C. Heine, who made his first Antarctic dives in 1989, and has subsequently spent 14 seasons on the ice, was concerned about the impact of the cold on the scrubber’s CO2 absorption efficiency, as well as freezing in the loop due to moisture, battery duration and function, display irregularities, accuracy and precision of all readouts and sensors, and potential solenoid and regulator issues.

Photo courtesy of Dr. John Heine.

Heine and his team, which included Dr. Jeffrey Bozanic, author of several books on rebreathers, tested the performance of seven rebreathers, specifically the AP Diving Inspiration, Inner Space Megalodon Legacy and Megalodon 15, the Poseidon Se7en, the Hollis Prism 2 and semi-closed Explorer rebreather (see footnote 2), and Expedition One’s Titan. Their goal was to evaluate the overall performance of regulators, valves, batteries, sensors, and displays both pre-dive and underwater, measure temperatures in different parts of the loop before, during, and after dives, and to evaluate the performance of the rebreathers’ scrubbers. They placed temperature sensors in various portions of the loop to quantitatively measure the temperatures over time.

The Dives

Heine’s five-person dive team conducted a total of 116 no-stop dives to a maximum depth of 130 ft/40 m on the seven rebreathers during the austral summer season in Antarctica (Oct-Nov 2016). The average depth of the dives was 85 ft/27 m, with an average dive time of 33 minutes, for a total of nearly 66 hours. They used air diluent in the rebreathers; low setpoints were 0.5 or 0.7, and the high setpoints were 1.2 or 1.3. Divers were equipped with 40 ft3/5.5 L bailout cylinders, which were also used for drysuit inflation. They also had a safety diver on open-circuit, and surface tender(s).

Dr. John Heine in Antarctica. Heine had his first dives in Antarctica in 1989. He has been going there fourteen seasons now.

The dives were staged from a heated hut, with a temperature of approximately 60° F/15.5° C, and a water temperature of 28.6° F/-1.8° C. The rebreathers were pre-breathed in warm air, either in the dive locker or in the heated hut. Pre-dive checklists were performed on all of the units.

Most dives were conducted in no current and were characterized as “low activity level.” The scrubbers were only used one-half of the manufacturer recommended time (at 4° C) on the advice of Scientist Emeritus and Retired Scientific Director of NEDU Dr. John Clarke, who sits on the USAP Diving Control Board. “Our dives were rarely longer than 40 minutes,” Heine said. “The limiting factor was the cold, and in some cases decompression, not the scrubbers.”

In addition, they performed dry tests where the rebreathers were pre-breathed in a warm shed or in cold ambient air temperatures of 5° F (-15° C) and then left in the cold for a period of two to three hours. Temperature data from the various portions of the loop were recorded and analyzed, along with qualitative observations on the function of the units. “It is eye-opening how fast things freeze up in air,” cautioned Heine, who was first certified in 1976 in Laguna Beach, CA.

The Cold Facts

The good news was that the rebreathers performed better than expected, with the exception of the Hollis Explorer. One hundred eleven dives (96%) were considered “successful,” which was defined as a complete dive without cause for ending or aborting the dive, or switching to bailout. Five dives (4%) required aborting or switching to bailout and ending the dive.

The Se7en, for example, had a few problems with its (galvanic) oxygen sensors; the automatic diluent valve (ADV) on the Inspiration had probable “freeze-ups” on two occasions, and the Explorer had a number of issues with the electronics, including a “bad cell” warning.

These results compare favorably with a 2017 study of open-circuit regulators (see footnote 3). Seventeen models of regulators from 12 different manufacturers were tested in Antarctica and yielded 65 free-flows in 305 dives (21.3%). By comparison, the USAP-authorized Sherwood Maximus regulators had a free-flow rate of only 0.17% during the period of 2007-2017.

The batteries and displays functioned well, except in very cold air temperatures of 5° F/-15° C. In the dry test runs in cold air, scrubber temperatures stayed relatively warm, but temperatures in the lids near the oxygen sensors were below freezing, which is not recommended by the manufacturer. Mouthpieces also froze shut.

In-water evaluations were somewhat mixed. The Megalodon 15 showed temperatures in the lid approaching the ambient water temperature of 28.6° F/-1.8° C, while the inhalation counterlung temperature was about 10° F/5 °C above ambient, suggesting slightly warmed gas being delivered to the diver. In the Prism 2, both counterlung temperatures were near the ambient water temperature, while the temperatures in the lid (near the oxygen sensors) and the central tube of the scrubber remained around 40° F/4.4° C. The exhalation counterlung temperature was right at the ambient water temperature in the Se7en, while the canister temperature was 6-20° F/3-11° C above ambient, similar to results in other rebreather models.

In the Titan rebreather, the scrubber and the lid temperatures remained relatively warm during the dives, while the inhalation hose temperature was close to ambient. In temperate water trials, the inhalation hose temperature was also close to ambient, which suggests that the rebreather was not delivering warmed gas to the diver. The team was not able to measure inhalation gas temperature with the available technology, nor were they able to measure the CO2 in the loop (temperature served as a proxy for absorption efficiency), so these results are unknown.


nspiration shows two dives, top and bottom of scrubber very warm (90 F), and the inhalation and exhalation hose temps. closer to ambient temp.

Poseidon Se7en.  Exhale counterlung at ambient water temp, scrubber canister 5-10 degrees above ambient.

In the Legacy Megalodon, four dives on two consecutive days, with a total scrubber time of 163 minutes.  Axial scrubber temperatures well above ambient, indicating active CO2 scrubbing.

Note that gas temperatures being delivered to the diver in open-circuit systems would most likely be less than the ambient water temperature, due to gas expansion and pressure drop from the second stage pressure of 150 psi above ambient to ambient. So, all CCRs delivered “warmer” gas to the divers compared to open-circuit, but generally not to an appreciable level. Heine believes that adding insulation materials to the canister and breathing loop hoses and/or counterlungs might help in keeping the breathing gas warmer.

As a result of the study, Heine is now incorporating the use of rebreathers into USAP’s diving standards. A first group of rebreather divers from the BBC, who will be filming seals, is expected next season. There will also likely be a project studying diatoms, which grow beneath the ceiling of ice and are easily disturbed by bubbles.

Note: Unfortunately, Global Underwater Explorers (GUE) divers planning to participate in GUE’s 2021 Antarctica Expedition will need to leave their rebreathers at home. The trip will be limited to open-circuit diving only, unlike Heine’s diving scientists.


1. Heine, J.N. and Bozanic, J. 2018. Evaluation of Closed Circuit Rebreathers for the National Science Foundation  US Antarctic Scientific Diving Program Diving for Science 2018: Proceedings of the AAUS 37th Scientific Symposium. 40-58.

2. Huish Outdoors acquired Oceanic and Hollis in 2017 and discontinued the Explorer semi-closed rebreather.

3. Lang, M.A. and J.R. Clarke.  2017. Performance of life support breathing apparatus for under-ice diving operations. Undersea Hyper. Med. 44(4): 299-308.

Additional Resources:

John Clarke Online:

Authorized for Cold Water Service: What Divers Should Know About Extreme Cold: https://johnclarkeonline.com/tag/en-250/

Information on scrubbers and the cold:

Primer on Scrubbers:


Michael Menduno is InDepth’s executive editor 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.

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My Deep Dive Into The Dunning-Kruger Effect

Tech diver Brendan Lund shares his personal diving journey from summitting Mount Stupid and descending into the depths of Despair on trimix, before finally beginning his ascent on the Slope of Enlightenment. No Kool-Aid was involved in the making of this story.

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by Brendan Lund
Images courtesy of Brendan Lund

Lund diving in Socorro, Mexico,

I started diving in 1996 as a poor student in South Africa. I absolutely fell in love with diving, and haven’t stopped since. After moving to the UK in 2001, I finally started earning money and was able to dive more frequently. At this time, the Red Sea was starting to boom, and I was able to book a full week of diving—including flight and accommodation—for as little as 350 GBP! Many trips later, I became interested in tech diving, as it was the happening thing, and in 2004 I decided to begin my tech journey with a leading agency. This also signals the start of my journey with the Dunning-Kruger Effect!

Grokking Dunning-Kruger 

I first saw the Dunning-Kruger effect graph a year or so ago and couldn’t stop thinking about its relationship to my diving. 

What is the Dunning-Kruger Effect? Here’s what Wikipedia has to say:

In the field of psychology, the Dunning–Kruger effect is a cognitive bias in which people with low ability at a task overestimate their ability. It is related to the cognitive bias of illusory superiority and comes from the inability of people to recognise their lack of ability.

As described by social psychologists David Dunning and Justin Kruger, the bias results from an internal illusion in people of low ability and from an external misperception in people of high ability; that is, ‘the miscalibration of the incompetent stems from an error about the self, whereas the miscalibration of the highly competent stems from an error about others’.

The graph below simplifies this concept—again, this is taken from the internet, but the wording pretty much sums up what I have been feeling throughout  this journey:

The less knowledge you have, the more confident you feel. The more you learn, the less confident you feel. 

The View from Mount Stupid

In 2005, I progressed from an advanced nitrox diver to a fully-certified advanced trimix diver. My instructor was a well-known deep diver at the time, and I was super impressed with the courses. I was at the point of Mount Stupid on the graph. These courses were not a pass/fail style of course; you just had to prove you could complete the skill once, and bam! You’re qualified! 

“Wow, I’m the man! I’ve passed my Advanced Trimix Course and dived to 100m.”

I dug out the photo below from a box in the shed. We had someone take an underwater photo of us celebrating our successful completion of our deco procedure course. As you may notice, trim was not a requirement at the time (I’m now hiding my face with embarrassment)! Apologies to my buddies in the photo; it was a while ago, and the instructor is the only one in reasonable trim!

Class celebrating the completion of a deco procedures course.

To say I was chuffed is an understatement! I immediately went tech diving as much as possible. In 2008, I decided to travel the world for a year—diving of course. I met many amazing people and dived everywhere; I also became an instructor with a well-known recreational agency. I was at the top of my game (or so I thought), although I still don’t think I had any trim! I mean, who needs trim, right?

On one of my adventures, I met a guy who was really interested in checking out a new agency that he had heard of. This would be the first time that I heard about Global Underwater Explorers (GUE). After much research and reading internet forums for GUE in 2000, I believe the Dunning-Kruger realisation phase of my journey began: I thought, “There is definitely a lot more to this!”

The Slope of Despair

I’m not going to lie; the more I looked into GUE, the more nervous I got, and the more I slid down the slope of despair. It took me a good six years to build up the courage to sign up for a Fundamentals class, and I showed up on that day feeling very confident in my brand new drysuit and my horseshoe wing. Wow, did I learn that I was way out of my depth! I was in trouble. It was so much harder than I had ever imagined. I don’t think it was so much the course that was hard, but that it was hard for me to overcome my ego and overconfidence.



I received a provisional “Tech Pass” [i.e., I qualified to take GUE’s Tech 1 or Cave 1], and it felt like I had failed! I was at the bottom of the Dunning-Kruger slope of despair.  Was I ever going to get it? I questioned whether I should go back to get my pass, and I have to thank my buddies Nikky and Darren for encouraging me to do so. After lots of practice and some gear tweaks, I felt like I smashed it, and achieved my Tech Pass! Was this the beginning of the slope of enlightenment? Things were starting to make sense!

The Slope of Enlightenment

I have now completed two more GUE classes—DPV1 and Cave 1—and am signed up for Tech 1 next year. The future looks bright! I dive as often as I can with like-minded divers, and I realize that there is always more to learn and areas where I can improve. I am hopeful that I am now on the Slope of Enlightenment; it certainly feels that way.

I highly recommend GUE to any divers that would like to work on themselves. It has definitely helped me on my diving journey, and I now look forward to many more years of diving and learning. I can’t wait to get involved in more projects and extend my skill set.

Additional Resources

It’s Never Too Late To Tackle Fundamentals


Brendan is an events manager based in London and (currently) dives mainly around the southwest coast of England. He started diving in 1996 in South Africa and has dived all around the world. He found a passion for cave diving a few years agohis favourite place to do this is Tulum, Mexicobut still loves wreck diving. Brendan is looking forward to the next challenge, with project work planned with Project Baseline, and Tech 1 is in his diary for next year in Croatia, since Covid-19 postponed it this year.

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