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The Economics of Choosing CCR Vs OC

How many “deep” open circuit dives would you have to conduct—you are using helium aren’t you?—to pay for a rebreather, training and necessary experience dives? It’s question that instructor evaluator Guy Shockey explores in detail in his analysis of the economics of rebreather versus open circuit scuba. Ironically, shortly before this article posted, the author informed us that helium prices in Western Canada had risen again and availability was limited. The result, explained Shockey, is that the number of dives to break-even is likely down 25%, or about 39 dives compared to 52 dives as calculated in his story. Welcome to what the gasworld magazine calls it, “Helium Shortage 4.0.” Time for InDEPTH’s Holiday Rebreather Guide!



By Guy Shockey. Images by Andrea Petersen unless noted.

Technical divers

I teach both open circuit and closed circuit Global Underwater Explorers (GUE) technical diving courses, and I am frequently emailed or messaged from students who have completed their Technical Diver 1 (Tech 1) course and fulfilled their experience requirement for further training. They ask me for advice as to whether they should move forward with Technical Diver 2 (Tech 2) or start down the CCR pathway with Closed Circuit Rebreather Diver 1 (CCR 1). 

There are several factors to consider when making this choice, but one of the biggest decisions concerns the relative cost of both pathways. The up-front cost of closed circuit rebreather (CCR) training appears considerable on the surface: you need to purchase the CCR and the associated parts and pieces to set it up as a GUE compatible system. I decided to do a little math and see at what point a diver would reach a break even point with their CCR purchase as opposed to conducting OC Tech 2 dives. 

To compare apples to apples, I also needed to include both CCR 1 and Closed Circuit Rebreather Diver 2 (CCR 2). This is important because, while CCR 1 will get you the knowledge and training to do your CCR 1 dives in the T1 range (max depth 51 m/170 ft w/30 minutes of deco), you will need CCR 2 training to move into the Tech 2 range (75m/250 ft with 60 min of deco). 

Costing Out The Options

I started with the actual cost of training, and for me, a Tech 2 class costs $2250. When I calculated the gas costs of a Tech 2 class, I used $1.75 cu ft of 21/35, $1.95 cu ft for 18/45 and $2.15 cu ft for 15/55. This could be much lower than in many places, and these costs are not going down. A typical Tech 2 class with me will see a 45 m/150 ft dive followed by a 60 m/200 ft dive and then a 75 m/250 ft dive. These depths and the times may vary from instructor to instructor, but this is likely a good starting point. 

With the volumes of the various gasses needed, adding three charters for the experience dives, and assuming the class had three students, so the instructor’s charges would be split three ways, I came to an amount just shy of $5,350 for costs needed to complete a T2 class.

In comparison, I then did the same calculations for a CCR 1 class. This included doing some quick math with respect to the cost of the actual CCR unit itself. This is usually the big “Holy Smoke” factor for divers choosing between T2 and CCR 1. The JJ-CCR itself is about $9,000, and then you need to add in the parts and pieces to make it GUE compatible, and by the time the smoke clears, you are looking at about $11,500. [Ed.Note: At the present time, GUE only offers courses on the JJ-CCR in a special GUE configuration.] I assumed you would repurpose your OC regulators that you would have used in your Tech 2 class, so that portion of the costs are a wash. 

Class costs for a GUE CCR 1 class are the same as a Tech 2 class, but associated costs are considerably less. For this reason, the CCR 1 course fee and incidental costs come to $2,970, assuming that the student rents their CCR cylinders, or $2380 less than a Tech 2 class. Thus, your initial outlay to take a GUE CCR 1 class would be in the neighborhood of $14,470.

This means that your choice to take CCR 1 over Tech 2 would require an additional $9120. 

After your CCR 1 course, and 25 experience dives on your JJ-CCR, you will be diving your CCR unit into your original Tech 1 range, with a significant cost savings per dive. One of the biggest benefits of diving a CCR is that gas costs are not that different regardless of whether you chose to dive to 45m/150 ft or 75m/250 ft. This means that, if you wish, every dive can be a technical dive.

In order to compare apples to apples, I wanted to take this one step further and see what the economics were of taking the JJ CCR into the Tech 2 range. Remember that the original choice was CCR 1 or Tech 2, and stopping your CCR training at the CCR 1 level would not give you the knowledge or training to safely dive into the Tech 2 range. There are some significant considerations when moving from the normoxic to the hypoxic range of technical diving, and the CCR 2 class includes much of what was previously taught in Tech 2. 

CCR and OC divers at EDGE 2.0 workshop at Maple Bay, British Columbia.
CCR and OC divers at EDGE 2.0 workshop at Maple Bay, British Columbia. Photo by SJ Alice Bennett

I have written about this before but, in a nutshell, if you have to bail out from a CCR 2 dive, you are then basically an open circuit Tech 2 diver, and you need all the same skills required as a Tech 2 diver, including bottle rotations. Hence the CCR 2 course is considerably more complex because it combines both open circuit and advanced closed circuit hypoxic dive training. 

The prerequisite to CCR 2 training is the requirement to perform at least 50 CCR 1 experience dives with half of them in the Tech 1 range. The good news is that these dives are a lot less costly than an open circuit dive to the same range. Fifty of these dives will cost you about $260 per dive (assuming you need a dive charter and rent cylinders) so at the outside, you will spend $13,000 on these dives. 

Now we need to add back in the cost of the CCR 2 course, and this training— including incidentals—will cost you in the range of $3913. Thus, to take your JJ CCR into the Tech 2 range, you will need the cost of the experience dives and the cost of the CCR 2 course. This will add an additional $16,913 to your initial cost difference of $9120 when you choose the CCR 1 over Tech 1 pathway. In a nutshell: you will need just shy of $26,033 more if you choose to move into the Tech 2 range. However, this would presumably be spent over a year or two.

This seems like quite a significant cost difference at first, and $26,03 is nothing to sneeze at for sure! However, now we need to start looking at what all your future diving is going to look like. 

Using an 18/45 trimix dive to 60 m/200 ft as a baseline “standard T2 dive,” and using all the original costs and volumes I used to calculate the Tech 2 class, I calculated each Tech 2 dive as costing about $731. At the same time, the equivalent CCR 2 dive will cost you about $200, with potentially $60 cylinder rental (ccr and bailout bottles). When the smoke finally clears, you will save about $500 per dive if you do them on your CCR and it would take you only 52 dives to make up your original cost differential! [Ed: Total cost to achieve CCR2 ($31,383) less T2 class cost ($5349)÷ $500/dive] Moreover, since it will really cost you about the same to do a CCR 2 dive than a CCR 1 dive (excluding bailout cylinders), all 52 of these dives can be done exploring some pretty remarkable sites that are outside of the range of the vast majority of divers. 

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The assumptions used in the calculations shown above are here:
CCR v OC Calculations

Doing these calculations was quite enlightening. I knew that at some point, it would make sense to choose CCR over OC for technical diving, even given the higher costs to “buy in” to CCR training, but I didn’t honestly realize that the break even point for a diver who chose the CCR 1 and CCR 2 pathway as opposed to the Tech 2 pathway would need only 52 dives to make back their investment!

The assumptions used in the calculations shown above are here: 
CCR v OC Calculations

There are a few other things to consider after your T2 or CCR 1 training also. 

Other Considerations

As I mentioned above, one of the coolest things about CCR diving is understanding that your oxygen use is independent of depth. It is a function of your metabolism, and it doesn’t matter how deep you decide to dive. The only factor that needs to be considered with respect to depth is the amount of diluent you need for your loop volume, the amount of bailout gas you need, and drysuit inflation. What this means when the rubber hits the road, is that every dive can be a tech dive where you are exploring outside the limits of the recreational diving realm! For me, this was a huge consideration: I wanted to see what most divers were not able to see, and this meant diving past the normal recreational limits. Basically then, my de facto technical diving increased substantially because cost was no longer such a limiting factor. All my “fun” dives could be technical dives!

From a logistical point of view, unless you need to use your bailout deco gas, the only gas you will need to use there is what is wasted during gas analysis! This means that your bailout deco gas lasts a longgggg time! This also helps when it comes to, “How many cylinders do you need to carry on the boat?” You can do a lot more diving with fewer cylinders, and this is not something to ignore when talking about T2 level dives!

I live in the Pacific Northwest, and the water temperatures here can be challenging depending on the time of year. There is absolutely no question that I am warmer when diving on my CCR. The air I am breathing is warmer and is not as dry. I most definitely notice this and stay warmer in colder water. 

Is There a CCR In Your Future?

Helium costs continue to rise, and availability is becoming more of a problem every day. This means that the break even point continues to come sooner, and the follow-on costs become more significant. This means that in our current world, for those with a desire to explore in the technical diving range, the decision to choose the CCR 1/CCR 2 pathway versus the T2 pathway becomes more straightforward!

There are several things to consider when deciding whether to choose the CCR or OC pathway past T1. Costs, logistics, helium availability—now and in the future—are just part of this equation. 

I think the CCR 1 pathway is likely the most pragmatic choice, but this requires a healthy initial investment and an understanding that you will likely need to complete CCR 2 down the road to have access to the deeper depths that T2 unlocks. There are a lot of considerations involved when entering the hypoxic gas realm and the associated skills required if things go sideways on these deeper dives. Frankly, I get a little nervous when I see divers moving into these deeper ranges with no CCR training specific to these depths. “You don’t know what you don’t know” is a very real consideration here. 

CCR 1 is likely the way of the future. The benefits are clear, and it unlocks many aspects of technical diving that fit well with our GUE exploration world. I have personally seen an increase in CCR students after T1 and look forward to seeing our technical world grow and evolve!

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To Be, or Not to Be a CCR Diver: How I made the Choice

InDEPTH asked new technical or CCR divers to tell us how they went about making the decision as to when and why to make the switch from open circuit. Here’s what they told us: To Be, Or Not To Be

Dive Deeper

InDEPTH: GUE and the Future of Open Circuit Tech Diving by Ashley Stewart

QUEST: CCR LEVEL 2 Enters The World by Guy Shockey

InDEPTH: The Thought Process Behind GUE’s CCR Configuration by Richard Lundgren

InDEPTH: Can Mouthpiece Retaining Straps Improve Rebreather Diving Safety? by Reilly Fogarty

Guy Shockey is a GUE instructor and instructor trainer who is actively involved in mentoring the next generation of GUE divers. He started diving in 1982 in a cold mountain lake in Alberta, Canada. Since then, he has logged somewhere close to 8,000 dives in most of the oceans of the world. He is a passionate technical diver with a particular interest in deeper ocean wreck diving. He is a former military officer and professional hunter with both bachelor’s and master’s degrees in political science. He is also an entrepreneur with several successful startup companies to his credit.

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Hydrogen, At Last?

In February, Dr. Richard Harris aka Dr. Harry and the Wet Mules conducted the world’s first hydrogen rebreather dive to a test depth of 230 m at Pearse Resurgence, New Zealand. The purpose of the 13.5 hour dive was to determine the practicality and efficacy of using hydrogen to improve safety and performance of über-deep scuba dives. Harris will present the work up and details of the dive at Rebreather Forum 4 in Valletta, Malta on 22 April. In preparation, we thought it useful to review some of the history and research regarding hydrogen diving. Here’s what you need to know.




By Michael Menduno. Header image: Dr. Richard Harris and Craig Challen at the entrance of Pearse Resurgence . Photo courtesy of Dr. Simon Mitchell.

🎶 Pre-dive clicklist: Hydrogen Song by Peter Weatherall, the singing scientist 🎶

Harris’s recent dive is the latest of an estimated 54 experimental hydrogen dives that have been conducted over the last 80 years by military, commercial and, yes, technical divers. It was the first reported hydrogen dive made on a rebreather, in this case, dual Megalodons connected by the bailout valve (BOV)—one charged with trimix diluent, the other with hydreliox (O2, H2, He). It was also the first hydrogen dive conducted in a cave.

The idea of using hydrogen to improve diver safety and performance on deep dives has been a long time in the making. The Swedish Navy began a program led by 26-year-old diving inventor and engineer Arne Zetterström (1917-1945)—think a young Lamar Hires, Bill Stone, or perhaps Jona Silverstein—who was the first to experiment with hydrogen as a possible deep diving gas during World War II. At the time, the United States had the only known helium reserves. And, because of its use for military “barrage balloons” filled with non-flammable lighter-than-air gas, the US had instituted the “Helium Control Act of 1927,” which forbade the export of helium. Zetterström’s mission was to determine if hydrogen was a possible alternative.

Zetterström, whose father was a Swedish naval architect, developed a method for producing hydrogen from ammonia. He had worked out the flammability issues (hydrogen gas is explosive when mixed with more than 4% oxygen), and calculated a rudimentary decompression plan for hydrox. Ultimately, he conducted six surface-supplied dives on hydrox 4/96 (4% O2, 96% H2) to: 40m/131 ft, 70m/230 ft, 110m/361 ft and 160m/525 ft, with one case of decompression sickness (DCS). Bottom times ranged from 10-25 min with 140 min of air and oxygen decompression. Tragically, Zetterström was killed on the 160 m dive in 1945, when tenders mistakenly pulled him up from depth without decompression.

It was nearly 40 years before interest in hydrogen as a diving gas was rekindled. At the time, commercial diving was getting deeper as North Sea oil production boomed, and commercial diving contractors were pushing the limits of heliox (an oxygen helium mix) diving as depths approached and exceeded 306 m/1000 ft. They believed that hydrogen might offer a solution. Hydrogen is half the molecular weight of helium, reducing breathing gas density, and research by Duke University’s Dr. Peter Bennett on trimix suggested that the narcotic properties of hydrogen might ameliorate the effects of High Pressure Nervous Syndrome (HPNS), which is a major limiting factor on heliox dives. 

Commercial Divers Do It Deeper

Pioneering French commercial diving contractor Comex (Compagnie maritime d’expertises) launched its hydrogen program dubbed Hydra in 1982. Beginning with animal experiments, over the next decade, Comex conducted a series of manned wet and chamber complex dives, Hydra II-Hydra X, to determine the efficacy of hydrogen diving. 

In February 1987, the Undersea Hyperbaric Medical Society held its 33rd workshop in Wilmington, North Carolina, titled “Hydrogen As A Diving Gas,” which included presentations by Comex. The following year, during Hydra VIII, four Comex divers and two French Navy divers successfully performed six days of work at 530 m/1738 ft on an offshore platform near Marseille with dramatically improved diver performance when compared to heliox diving. 

Comex saturation divers working on an offshore platform at 530m depth breathing hydreliox.

In 1991, Comex conducted a final record chamber dive to 701 m/2300 ft at its Marseille headquarters. Serendipitously, as then publisher and editor-in-chief of aquaCORPS Journal, I was invited to witness the dive, which was in progress in the Comex chamber complex. Heady stuff indeed! Special thanks to decompression engineer, JP Imbert, who worked at Comex at the time, and diving safety officer George Arnoux who made that possible.

Following the UHMS Hydrogen Meeting, the US Navy’s Naval Medical Research Institute (NMRI), in Bethesda, Maryland, began a program that lasted more than a decade (1990-2001) researching hydrogen under the direction of research physiologist Dr. Susan Kayar. Kayar and her team showed that breathing hyperbaric hydrogen had no ill biochemical effects on mammals that had been previously overlooked.

Next they demonstrated the feasibility of “biochemical decompression,” aka biodec, which reduced the incidence of DCS in in animal test subjects following hydrogen dives by roughly half. With a human biodec protocol, divers would take a capsule of special mammal-friendly, H2-eating gut bugs—think probiotics—which would consume the H2 gas and convert it to methane that would then be released to the atmosphere through the path of least resistance. Small wonder that Dr. Kayar, who measured flatulence from pigs and rats decompressing from hydrogen, became known as the “Queen of Farts.”

Susan Kayar aka the “Queen of Farts”. Photo courtesy of S. Kayar

Comex and the research by the US Navy demonstrated that hydrogen could significantly improve the safety and performance of working divers, and in doing so extend their range, much as the introduction of helium breathing mixes has been able to greatly improve diver safety and performance over deep air diving. Unfortunately, hydrogen was very expensive to mix and handle in a saturation diving environment, and it arguably arrived on the scene too late.

By the late 1980s, the commercial diving industry was already transitioning to robotics, especially for deep diving, due to the economics—it was far less expensive and safer to put a remotely operated vehicle (ROV) at depth for many tasks, instead of a diver. As a result, hydrogen was never “operationalized” as a diving gas, and has remained an exotic vestige of hyperbaric research in search of an application.

Bring on The Tekkies

Hydrogen was on the minds of tech pioneers during the emergence of the “technical diving revolution” i.e., the adoption of mixed gas technology, in the early 1990s. Legendary cave explorer Sheck Exley cited hydrogen in an interview I did with him for aquaCORPS,“Exley on Mix,” in the fall of 1991. Exley had already made several sub-260 m/852 ft dives using trimix at a time when the majority of the sport diving industry would have been hard pressed to spell N-I-T-R-O-X, let alone know what it was used for. Ironically, that was the year that Skin Diver magazine editor Bill Gleason ingloriously dubbed nitrox the “Voodoo Gas,” a moniker that could arguably better be applied to hydrogen, whether hydrox or hydreliox.

Sheck Exley at Zacatón in the early 1990s. Photo from the aquaCORPS archives

As Exley explained, “From what I’ve been learning, there seems to be some real potential for hydreliox, though no one has looked at its use for deep bounce dives. With the kind of compression rates that I was dealing with at Mante, you need the heavy nitrogen to avoid HPNS, but I’d rather have the hydrogen.” 

You may be surprised to learn that Harris and the Wet Mules are not the first technical divers to conduct an experimental dive with hydrogen. That distinction goes to diving engineer Åke Larsson, and six tech diving colleagues. Fortuitously, Larsson worked at the Hydrox lab Swedish Defense & Research Institute under Dr. Hans Örnhagen. 

In 2011, in collaboration with the Swedish Diving History Society (SDHF) and Royal Institute of Technology Diving Club, they formed the Hydrox Project led by fellow techie Ola Lindh, with the goal of revisiting the work of Zetterström. Specifically, they focused on developing a mixing station, procedures and measuring system, and investigated flammability suppression, in the hopes of recreating Zetterström’s 40m dive.

Åke Larsson and colleague prepare for a 42 m hydrox dive. The yellow cylinder contains hydrox 4/96. Photo courtesy of Åke Larsson

In July 2012, the seven Hydrox Project divers each completed a single hydrox open circuit dive to 42 m/138 ft in an isolated quarry. The divers descended on air back gas, switched to the hydrox 4/96 stage cylinder at depth and breathed for five minutes, switched back, and then began a padded deco schedule on air, no oxygen for operational simplicity, using an extrapolated ZH-L16 algorithm. According to Larsson, “Breathing hydrox was a surprisingly pleasant experience! We planned the dive using air, so I was slightly narked but feeling well at 42 m. When we switched to hydrox gas, it felt cold but almost slippery and very, very easy to breathe compared to air. My brain cleared up in less than a minute and the nitrogen narcosis was gone.” 

Where Art Thou H2?

Though the Hydrox Project dives were technically not tech dives, and not very deep, there is reason to believe that hydrogen could improve diving safety and performance on über-deep untethered dives. First, and most importantly, hydrogen can improve the work of breathing (WOB), which is a major risk factor on deep dives.

The gas density of trimix 4/90 (4% O2, 90% He, balance N2) at 250 m/816 ft is 7.3 grams/liter, considerably above the 6.0 g/l threshold where the risk of a negative outcome dramatically increasesNote: it is believed that a high WOB killed Dave Shaw who suffered respiratory insufficiency during a 270 m/880 ft dive at Bushmansgat. With half the molecular weight of helium, hydrogen could reduce gas density to safe levels resulting in lowered work of breathing. For example, the density of hydreliox 4/30 (4%O2, 30% H2, balance He) at 250 m is 4.56 g/l, equivalent to breathing normoxic trimix 21/35 at 40 m.

Hydrogen, which is narcotic at deep depths (PH2≥ 15-20 bar), has also been shown to ameliorate HPNS, which is another major limiting factor at depth. And with market interest in hydrogen as a fuel source on the rise, the gas is plentiful, and cheap relative to helium, though mixing costs could be pricey.

However, there remains a HUGE caveat. Though technical divers were successful in adapting helium-based mixed gas technology to scuba diving, the situation with hydrogen is completely different. Helium diving was well established in the military and commercial diving communities by the late 1980s/early 1990s, and the technical community was able to draw on that experience. That’s simply not the case with hydrogen diving, which has not been operationalized, and most of the research has dealt with saturation diving.

In fact, there are significant challenges that must be addressed if self-contained hydrogen diving is to be possible, let alone successful. These include the real risk of fire and explosion, both above and below the surface, respiratory heat loss—hydrogen has about 3x the specific heat of helium and could lead to acute respiratory heat loss (RHL), followed by dyspnea, cough, and hyper-secretion; its high specific heat also impacts scrubber efficacy, particularly in cold water. Then there’s H2 to He isobaric counter diffusion, hydrogen narcosis. Oh, and the issue of decompression, which according to one expert may be the least of one’s worries {Ed. note: Because the other factors would likely kill you first!], and then there’s the matter of a suitable breathing platform. It’s a formidable list.

The Wet Mules at Pearse Resurgence for their February 2023 expedition. Photo courtesy of Simon Mitchell

Dive Like A Mule

The Wet Mules have been unrelenting innovators in their quest to explore Pearse Resurgence, a project that Harris first became involved with in 2007. Ironically, in 2012, a few months before Larsson and his team made their historic 42 m hydrox dive, Dr. Harris was explaining to the delegates at Rebreather Forum 3.0, in Orlando, Florida, why he and team mate Craig Challen were giving up on open circuit bailout at Pearse—it required some 28 cylinders each to bailout from a 220 m/718 ft dive with 30 minute bottom time. Instead the pair of push divers planned to dive dual back-mounted Megalodon rebreathers connected at the BOV—a configuration they still use today. They rejected sidemount bailout rebreathers due to poorer work of breathing (WOB). They have also worked with O’Three to adapt suits and electric heat to stay warm in the chilly 6ºC/43ºF Pearse waters, and created a system of decompression habitats in the cave to make the decompression safer, and more manageable.

One could surmise, it was only a matter of time before ‘Dr. Harry,’ who is a  deep diving anesthesiologist after all, would feel compelled to hit the H2. Feeling lucky today Punk?

Craig Challen helps Dr. Harry gear up. Note the dual Megalodon. Photo courtesy of Simon Mitchell

Harris will be presenting his report on his historical 230 m hydrogen rebreather dive at Pearse at the closing banquet for Rebreather Forum 4, in Valletta, Malta 22 April. His talk will be videotaped. He and Dr. Simon Mitchell, who was present with the Mules for the dive, is also preparing a paper for the Journal of Diving and Hyperbaric Medicine, and Harris will prepare a paper for The RF4 Proceedings, which will be issued in the fall.

Hydrogen Dreamin’

It is uncertain whether we’ll see a team of NIXIE tech divers—you know who you are— exploring a newly discovered 460 m/1500 ft deep shipwreck, supported by diving bells and an ROV in the next 10-20 years—think Britannic expedition on steroids! However, as tech dives continue to get deeperthe ten deepest cave dives today average 284 msw/926 fsw (adjusting for altitude and freshwater) or 75m/246 ft deeper than those of the 1990s thanks to rebreathers, while the deepest shipwreck dives today average 176 m/576 ft or 55m/180 ft deeper than those of the past it is possible that we will see limited use of hydrogen for special, well-funded tech projects.

It is perhaps more likely that one day soon, clandestine military divers will be locking out of a subsea platform wearing dual or triple H2-enabled rebreathers to carry out some über-deep mission—though we will surely never know.

Then again, hydrogen may well just remain another geeky diving dream that proved to be a dead end, albeit one that inspired us to continue think big and boldly about underwater exploration, and helped increase our understanding and knowledge of what is required for humans to safely breathe underwater, and dive deeper, and stay longer. Isn’t that what diving is all about?

Below please find a selection of curated hydrogen diving articles and resources. We hope you find them useful. And do consider coming to Malta to hear Dr. Harry’s talk. It will be historic.—M2

Rebreather Forum 4

Playing with Fire: Hydrogen as a Diving Gas

As every tekkie knows, helium is essential for deep diving due to the fact it’s non-narcotic and offers low breathing gas density. But it’s conceivable that hydrogen may one day become a part of the tech tool kit for dives beyond 200 m/653 ft, by virtue of the fact that it’s light, a little narcotic and offers the possibility of biochemical decompression. Diver Alert Network’s Reilly Fogarty has the deets.

High Pressure Problems on Über-Deep Dives: Dealing with HPNS

If you’re diving beyond 150 m/490 ft you’re likely to experience the effects of High Pressure Nervous Syndrome (HPNS). Here InDepth’s science geek Reilly Fogarty discusses the physiology of deep helium diving, explains the mechanisms believed to be behind HPNS, and explores its real world implications with über-deep cave explorers Dr. Richard “Harry” Harris and Nuno Gomes. Included is a list of sub-250 m tech diving fatalities.

The Case for Biochemical Decompression

How much do you fart during decompression? How about your teammates? It turns out that those may be critical questions if you’re decompressing from a hydrogen dive, or more specifically hydreliox, a mixture of oxygen, helium, and hydrogen suitable for ultra-deep dives (Wet Mules, are you listening?). Here the former chief physiologist for the US Navy’s experimental hydrogen diving program, Susan Kayar, aka the ”Queen of Farts” gives us the low down on biochemical decompression and what it may someday mean for tech diving.

Operation Second Starfish: A Deep Diving Novel of Submarine Rescue, Science, and Friendship

You read about the science of hydrogen diving last month in a “A Case for Biochemical Decompression,” by former U.S. Navy researcher, Susan Kayar. Now read her science fiction: where experimental diving may one day take us! Retired scientific director of the Navy’s Experimental Diving Unit (NEDU), John Clarke reviews Kayar’s new novel, “Operation Second Starfish.“


NDRI: Arne Zetterström and the First Hydrox Dives by Anders Lindén and Anders Muren. Swedish National Defence Research Institute. 1985

H2HUBB:  The History of Hydrogen

InDEPTH: Diving Beyond 250 Meters: The Deepest Cave Dives Today Compared to the Nineties by Michael Menduno and Nuno Gomes.

InDEPTH: Maintaining Your Respiratory Reserve by John Clarke

John Clarke Online: Hydrogen Diving: The Good, The Bad, the Ugly (2021)

Hydrogen Diving – A Very Good Year for Fiction (2018)

Diving with Hydrogen – It’s a Gas (2011)

Undersea Hyperbaric Medical Society: Hydrogen as a Diving Gas: Proceedings of the 33rd UHMS Workshop Wilmington, North Carolina USA (February 1987)

Michael Menduno/M2 is InDepth’s editor-in-chief and an award-winning journalist and technologist who has written about diving and diving technology for more than 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, and he produced the first tek.Conferences and Rebreather Forums 1.0 & 2.0. In addition to InDepth, Menduno serves as an editor/reporter for DAN Europe’s Alert Diver magazine, a contributing editor for X-Ray mag, and writes for He is on the board of the Historical Diving Society (USA), and a member of the Rebreather Training Council. 

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