Diving

Saturation Diving for Marine Science

In 2018, eight years after the disastrous explosion of the BP Deepwater Horizon Oil Drilling Rig, I was invited to speak at the Gordon Research Conference (GRC). The conference topic was “The Functional Roles of Mesophotic Coral Reefs in the Anthropocene Mesophotic Coral Reef Ecosystems.” It was held at Bates College in Lewiston, Maine.

The term mesophotic refers to the “middle light” region of the ocean, generally assumed to begin at about 30 meters seawater (98 feet sea water, fsw) and reaching to 150 meters (490 fsw.) [Exact values vary depending on location; in clearer ocean water where deeper water corals grow, light penetrates deeper (up to 200 meters) than in sediment-filled water.] Beyond the mesophotic zone, the available light is too low to support photosynthesis.

Mesophotic Zone image generated by OpenAI’s DALL-E 3 and modified by the author.

As the Scientific Director of the Navy Experimental Diving Unit, I spoke on the topic of “Saturation Diving as a Tool for Mesophotic Depths and Beyond.” Ten years before that, I’d spoken at an American Academy of Underwater Sciences (AAUS) Conference on “What the Navy Can Contribute to Scientific Diving.” So, the GRC talk was a continuation of the theme.

Well, my GRC talk was met with polite skepticism. To be fair, some marine biologists, such as Dr. Sonia J. Rowley, want to be hands-on with their research subjects. Having trained to be a science diver, I fully understand that. But in my opinion at the time, sometimes you just need a professional, well-equipped diver to do the dangerous dives for you.

CCR Bounce Dives

For a fictional example, an independent minded researcher plans on using a closed-circuit rebreather (CCR) to make a single dive to 160 meters. The purpose of the dive is to transplant deep water corals for 15 minutes working on the bottom. The breathing gas planned for the work on the bottom is 5% oxygen, 83% helium, and 12% nitrogen, maintaining a PO₂ of 1.1 atmospheres at depth, 1.3 PO₂during decompression.

The time cost for those 23 minutes of bottom time (15 min of working time) is 9.3 hours, mostly spent decompressing[1] during the ascent back to the surface. (If you’re lucky enough to decompress on a wall coming up, then you’ve found the perfect dive spot!)

The next day, the same dive is repeated, implanting coral in another site a few yards away from the first. After two days of diving, 30 minutes of work on the bottom will have been completed, and about 18 hours will have been spent unproductively, hanging on a line, decompressing, exposed to the elements, at constant risk of life support (CCR) failure and the need for bailout, and deterrence of curious marine predators.

Saturation Diving

The alternative to decompression-intense “bounce” dives, is saturation diving from a habitat under pressure, a home away from home. Why spend nine hours hanging on a line when those same hours could be spent working at depth?

Of course, a saturation diver still must decompress, but they only do it once, at the end of the work-filled mission which can last days or weeks.

The 37 day diving profile for a saturation dive to the pressure equivalent to 1500 fsw. Author’s copy.

Living Under Pressure on the Surface

One method which works well for the U.S. Navy and oil-well workers around the world, is to descend to the ocean bottom under pressure in a diving bell, and once bell pressure and sea water pressures equalizes, swim or walk to the worksite. At the end of the shift, divers return to the surface ship or platform, still under bottom pressures, and lock in to the pressurized living chambers.

NEDU’s Saturation Detachment hyperbaric living chambers connected to the diving bell. Photo courtesy of NOAA.

Saturation diving bell being lowered through the diving well of a support vessel, into the deep water of the Gulf. Photo courtesy of NOAA.

NEDU’s saturation diving bell at 722 fsw at 1:24 in the afternoon. Photo courtesy of NEDU.

US Navy Saturation Divers planting coral at 100 meters depth in the Gulf of Mexico. Photo courtesy of C-Innovation.

This US Navy assisted coral reef restoration dive series was described in a 2024 NOAA publication.

NOAA used US Navy Sat Divers on one coral propagation mission, and rebreather divers on another mission.

Upon a repeat visit of a NOAA vessel to the area where Navy Sat Divers implanted deep corals, there was a 95% survival rate of a diverse genetic population of corals.

Living Under Pressure on the Sea Floor

There has been a rich history of aquanaut habitats placed on the sea floor. As a graduate student at Florida State University, I spent the summer in Panama City, Florida diving with retired Navy divers and fellow graduate students in the Navy, NOAA, and State University System Institute of Oceanography funded Scientist in the Sea (SITS) Program.

One diving exercise was to resurface the SEALAB I habitat sitting in 60 feet of seawater. We were very hands on with the habitat, which now sits at the Museum of Man in the Sea, in Panama City Beach.

Sealab 1(1964, 194 fsw, 59 meters)

Sealab 1. At the Man in the Sea Museum, Panama City Beach, FL.

Sealab I was originally deployed in Bermuda in 1964 at 194 fsw (59 msw).

Helgoland (1969, 25 meters)

Helgoland. By Klugschnacker – Own work, CC BY-SA 3.0

The next habitat I encountered was Helgoland, an uber-sized German habitat, decommissioned at the end of the 1970s. It was displayed outside GKSS Research Centre, Geesthacht, Germany where another Navy scientist and I were conducting physiological studies on a trimix dive to 450 meters sea water. Peter Bennett from Duke University was proving once again how Trimix, (oxygen, helium, and nitrogen), could suppress the High Pressure Nervous Syndrome.

Aquarius Reef Base

At one time during my career at the Navy Experimental Diving Unit, I was a part of the certification board for the Aquarius habitat. I got to dive on it and in it, in an inspection capacity. But regrettably, I never got to saturate in it.

Other habitats

The Sealab projects did not end with Sealab I. The Navy followed up with larger and more ambitious habitats, known as Sealab II (1965, 205 ft, ~62 meters), and Sealab III (1969, 610 feet, ~185 meters). Then there was La Chulupa (1972, 20 meters, 66 feet), Tektite (1969, 49 feet) and Hydrolab (1970, 50 feet.)

Even today the La Chulupa habitat, renamed Jules Undersea Lodge, rests in thirty feet of seawater in a shallow lagoon. Touted as an underwater hotel, it accepts visits or stays by scuba divers. (As an instructor in SITS 2000, I visited, but did not stay.)

A 60-year Time Jump

From the U.S. Navy’s Sealab series of saturation dives to today is an approximately sixty-year leap into the future. In that time span, engineering and manufacturing improvements have advanced two generations. Human’s saturation experience at depth has advanced from 65 feet to over 2000 feet. As a result, the new generation of Deep’s undersea habitats promises to be a marvel to behold.

Concept visualization of Deep’s expandable Sentinel habitats.

Advances in Breathing Apparatus

There’s not much point in living underwater if you can’t step outdoors. Underwater breathing apparatus have likewise made great advances over the last 60 years. The greatest advance is in electronically controlled closed circuit rebreathers; known categorically as e-CCR.

Diver Burden

I don’t know of any diver who enjoys being burdened with a sometimes-bulky rebreather, plus large cylinders for bailout gas, and offboard cylinders for decompression gas mixes. But their survival depends on it. All that gear is required to safely accomplish a few minutes of useful work at depth.

CCR Bounce diver Dr. Sonia J. Rowley: multiple gas bottles on person for gas switches on way to the bottom and back, plus open-circuit bailout gas for 10 hours in case of rig failure or floodout. A depth of 200 msw (650 fsw) or more, is achievable with modern e-CCRs, although not recommended.

Sonia J. Rowley at depth. Photo by Dr. Dan Barshis in Indonesia, Wakatobi, 2023.

One solution is to dive with two or more rebreathers, one being a backup. That may be an improvement, but has not guaranteed safety in all situations.

The Case for Underwater Habitats

As Aquanauts have opined through the years, there is nothing more enjoyable than waking up, fixing a hot breakfast, putting on your minimal dive gear, and jumping into the water to work as long or as little as you wish. No hanging on a line in cold water to decompress, no wave action, just becoming as close to an ocean inhabitant as is possible for humans.

As the Deep company states, humans can become aquatic, once again.

There are no persons better equipped to describe the newest undersea habitat concept than those interviewed here by PADI.

The January 2026 PADI interview with Deep’s Dr. Dawn Kernagis, Norman Smith, and Roger Garcia.

The future of deep-ocean science may depend less on how deep we can dive than on how long we can remain. When expertise is embedded at depth—unhurried, observant, and continuous—the ocean stops being a hostile place briefly visited and becomes a working environment shaped around human capability. In that sense, saturation aquanauts are not relics of an experimental past, but early examples of a new kind of professional: knowledge workers operating under pressure, where sustained presence, not momentary endurance, defines both safety and success.

[1] Decompression model: Buhlmann ZH-L16C; Conservatism: Gradient factors (50/75)

Thank-you Sylvia Earle, the Lady of the Sea

In 2024, I met renowned marine biologist Sylvia Earle at the NOGI Awards in Las Vegas, expressing gratitude for her past mentorship in 1972. Her impact on aspiring divers has been profound, inspiring my shift to studying deep-sea diving physiology.

A chance meeting in 2024 gave me the rare opportunity to personally thank a diving scientist of unbounded fame, Sylvia Earle. Recently, at the 2024 Academy of Underwater Arts and Sciences NOGI Awards in Las Vegas, I found myself in the center of the assembled NOGI Awardees—both old and new. And right in front of me, was Sylvia.

Sylvia Earle

For those who don’t know, Sylvia Earle is an American marine biologist and oceanographer. While I call her The Lady of the Sea, she is more commonly called Her Deepness, or The Sturgeon General. Time Magazine named her their first “Hero for the Planet.”

According to Wikipedia, she has been a National Geographic Explorer at Large since 1998, and was the first female chief scientist of the U.S. National Oceanic and Atmospheric Administration (NOAA).

But I came to know Sylvia for a more humble reason: her simple act of sharing with young, aspiring divers.

Academy of Underwater Arts and Sciences

I had come to Vegas specifically to help diver and author Jeffrey Bozanic celebrate his NOGI award for diving education. The NOGI has been described by James Cameron, also a NOGI awardee, as the Oscar of the underwater world.

Jeffrey Bozanic giving his NOGI acceptance speech.

But much to my surprise, being one of the shorter attendees at the yearly photo op, I found myself standing behind Sylvia Earle. She was wearing her signature turquoise jacket.

I touched her shoulder and said, “After the photo, I want to tell you something.”

She nodded with a smile, “Sure.”

Scientist in the Sea

After posing and taking photos, I told her that over fifty years ago, in 1972, she had been a guest lecturer to our graduate science divers class in Panama City, Florida. We were in the second class of the NOAA, State of Florida, and Navy-funded Scientist in the Sea (SITS II) Program run by Captain George Bond, Wilbur Eaton, and others at the Navy base in Panama City.

Captain George Bond, M.D., 1972

Wilbur Eaton and a SITS student.

Back then, I had planned to be a marine biologist specializing in the effects of high pressure on the physiology of deep-sea organisms. So, having Sylvia Earle talk to our small class of divers was a dream come true.

Vegas

In Vegas, I told her my research path eventually shifted to human deep-sea diving physiology. Still, I will always be indebted to her for spending a day or two teaching us how challenging but rewarding a career in marine biology can be.

I can only speak for myself, but as a young diver, I was a little star-struck.

And now, many years later, I am thankful for the chance to let her know that we young divers greatly appreciated being taught by a pioneer in science diving.

Sylvia Earle, Ph.D. and Dan Orr at the Academy of Underwater Arts and Sciences NOGI Awards Gala, Las Vegas, 2024.

Lede photo credit: Outsideonline.com.

Demystifying Rebreather Scrubbers, RF4 Malta

Rebreather Forum 4 in Malta, organized by Michael Menduno, featured presentations on advanced rebreather diving techniques, including Dr. John Clarke’s talk on CO2 scrubbers, emphasizing safety, equipment selection, and individual diver variations. Presentations are accessible online.

Rebreather Forum 4, held in 2023 in Malta was yet another Herculean undertaking by Michael Menduno, the executive editor of Global Underwater Explorer’s (aka GUE) InDepth magazine and various international publications (see the above link for details.) Michael was the journalist who coined the term ‘technical diving”, and also created Aquacorp Magazine.

I’ve known and appreciated Michael for decades and gave presentations at his Rebreather Forums 2 and 3. My role on the RF4 Science Panel was to help select the best speakers for the Forum, to herd cats when necessary, and to speak.

The Book

Of course, with a new book (basically a textbook) on one of the most mysterious and technical aspects of rebreather diving, I spoke on the subject of “Demystifying Scrubbers”.

Breakthrough can be found on Amazon in paperback or Kindle, or elsewhere in ePub format.

Photo courtesy of *Axel Schoeller* (1963-2023)

Presentation Description

Here, I’ve borrowed Menduno’s own words describing my talk.

Plunge into the intricate world of rebreather diving safety and techniques with retired scientific director of the US Navy Experimental Diving Unit (NEDU) and author, Dr. John Clarke, who illuminates the inner workings of rebreather CO₂ scrubbers, based on extensive research work by the US Navy and his own modeling efforts. This talk unveils the critical aspects of CCR diving gear selection, especially focusing on the importance of rebreather CO₂ scrubbers, soda lime quality, and the proper maintenance of canister duration to ensure diver safety.
From the influence of cold water on CCR diving equipment to the vital role of physiological variation among divers, discover how individual differences significantly impact rebreather canister duration and CO₂ absorption rates. Engage with real-life scenarios and experiments that shed light on the potential dangers of compromised soda lime; explore the implications of using indicating soda sorb without proper Navy notification (leading to catastrophic failures in rebreather functionality). Moreover, the discussion covers simulated physical models that offer insights into the dynamics of CO₂ absorption in rebreather diving. The models emphasize the importance of understanding your CCR diving equipment and recognizing when changes, no matter how slight, in soda lime granule size or distribution might signal a risk. This video is an essential watch for any rebreather diver seeking to deepen their safety knowledge, highlighting the blend of technical expertise, physiological awareness, and practical vigilance required to navigate the underwater world securely.
Michael Menduno

Video

The video of my entire talk can be viewed here.

All RF4 Presentations

All of the RF4 presentations are available at this RF4 link. It is chock full of the best information available, from the best presenters in the field of Rebreather Diving.

Professional Diving, Truth, and the Uncertainty Principle

The post explores the theme of uncertainty in various contexts, from weather predictions to diving safety. It discusses how multiple measurements can lead to confusion rather than clarity, using Heisenberg’s Uncertainty Principle and Segal’s Law. Ultimately, it emphasizes the importance of human judgment in interpreting uncertain data for safe decision-making.

Is anything known for sure?

Heisenberg’s Uncertainty Principle applied to quantum events avows that there is no certainty until you look. Well, this morning, I looked, and I’m just as confused as ever.

It was a chilly morning in late November. As we warmed up with coffee, I wondered how cold it was outside. So, in the modern style, my wife and I checked the Weather Channel on our phones. One indicated it was 47°F, but the other showed it was 48°F.

That can’t be, I said. So, with identical phones side by side, both tuned into Panama City Beach, Florida weather on the Weather Channel, one phone said it felt like 45°F, and the other said it felt like 43°F.

As Charlie Brown would say, “Good grief.”

Wanting to find some agreement among our devices, I checked a nested set of humidity and temperatures sensors grouped together in our kitchen. Humidity indicators are notoriously inaccurate, yet amazingly, the measured humidity was in reasonable agreement. But inside temperature varied from 70.3°F to 72.8°F.

According to Segal’s Law, “A man with a watch knows what time it is. A man with two watches is never sure.”

This aphorism is falsely attributed to Lee Segall of KIXL, now KGGR in Dallas. Regardless of the source, it is often repeated because it makes such good sense. If you multiply the number of devices three times, as above, the situation is no more precise. (But that’s where statistics comes in, I suppose.)

Giving up on simple things like local environmental parameters, I turned to the latest news on the VAERs update for the vaccines.

I wish I hadn’t. Yes, there is a chance you’ll be fine, but there’s also a small chance you’ll have heart problems and even a small chance you’ll die.

Frankly, my one-time shot at slot machines and the roulette table in Vegas did not end well. So, is there anything we know that can be guaranteed accurate?

I’ve spent a long Navy career in diving science, so I know there are serious certainties there. If you consume more air than is in your scuba tank, you’ll drown. If you stay down too long and surface too quickly, you’ll get the bends, aka decompression sickness.

But what if I use a decompression computer to plan my dive and follow its guidance to the letter? Unfortunately, there’s still a chance you’ll end up in a treatment chamber. Both people’s health and the water environment change constantly, and no decompression algorithm is perfect, or omniscient.

From an engineer’s perspective, the tensile strength of a bolt is known within strict limits. If the force applied to that bolt exceeds its limits, then bad things might happen. Buildings might fall, or planes might crash. Or your muffler might fall off.

It’s hard to know what the effect of a broken bolt will be unless you understand precisely the function of that bolt. There is uncertainty in the outcome of a bolt breaking.

Uncertainty vexes some engineers to no end. I’ve watched them squirm as I reveal the role of statistics and probability in acceptance decisions about diving equipment. People are not bolts whose tensile and shear strength can be measured. As Heisenberg predicted (out of context), a dive outcome cannot be predicted with certainty.

Equipment Testing

The same thing applies to diving equipment. The Navy Experimental Diving Unit is entrusted with determining the safety and suitability of underwater breathing apparatus. Both physiologists and engineers envision a line in the sand for a given water depth and diver breathing rate.

If a UBA exceeds that line during testing, it should be rejected for military use. Right? After all, a limit is a limit.

Test and Evaluation Laboratory, Navy Experimental Diving Unit, Panama City, Florida. Photo by Stephen Frink.

Well, not exactly. When translating engineering limits into human terms, things get messy. If a published limit is exceeded, just like taking the COVID vaccine, some people will fare well, while others may pass out. In other words, failure is classified as the probability of an untoward event where untoward translates to anything that threatens a diver or a diving mission.

For any given dive, and any given diver, the probability of a dive failure cannot be known precisely. Dive failure, like decompression sickness, is probabilistic.

One type of untoward event: Ice inside a second-stage scuba regulator.

To illustrate, the following table and text are from NEDU Technical Report 16-04, Physiological Event Prediction in Evaluations of Underwater Breathing Apparatus, October 2016.

Usually, a UBA evaluated at NEDU is suitable for most diving depths and any foreseeable work/ventilation rate, as shown in Table 1.

The only time that limits were exceeded was at the greatest depth and ventilation rate.

But what if the data had revealed a slightly larger “out of limits” region, as in the next table? What decision regarding safety would then be made?

In this hypothetical case, human judgment is required. It is not sufficient to declare the diving equipment unsafe for use. It simply means divers need to pace themselves when working and breathing hard near a depth of 200 feet. Reducing their workload enough to slow their breathing to 62 liters per minute or less (still a high ventilation rate) is a safe way to keep the UBA within limits.

This is nothing new. Every salvage diver knows to occasionally interrupt hard work periods with periods of rest. Catching your breath is kind of important.

Limits are not absolute

As a person with too many watches, or thermometers can attest, you can’t be sure what all the various goal numbers and limit numbers mean. Instead, collectively they should be used as a guide to safe diving.

Whether you’re a sport diver or professional, if an underwater breathing apparatus is functioning normally but doesn’t meet all of the EU (EN250) or U.S. Navy engineering limits under all possible testing conditions, that doesn’t mean it’s not a useful piece of diving gear. You just have to use it judiciously. After all, good human judgment is always required for safely operating life support equipment.

It is a wise diver who remains mindful of their life support system’s limitations and plans their dive to stay within those limitations. That way, the probability of experiencing an untoward event is minimized.

Maintaining Your Respiratory Reserve

The following is a reprint from InDepth: Digital Scuba Diving Magazine by Global Underwater Explorers.

Published on September 6, 2019 By InDepth

by John Clarke

“*JJ on his JJ*.” *Photo by Andreas Hagberg.*

Just like skeletal muscles, respiratory muscles have a limited ability to respond to respiratory loads. An excellent example of this is a person’s inability to breathe through an overly long snorkel (Figure 1.) Our respiratory muscles simply aren’t strong enough to overcome the pressure difference between water depth and the surface.

*This doesn’t work. Her respiratory muscles are not strong enough.*
Illustration by Cameron Cottrill.

The primary respiratory muscle is the diaphragm, (the brown organ lying below the lungs in Figure 2.) The diaphragm is designed for low-intensity work maintained 24/7 for the entirety of your life.

Like the heart muscle, its specialty is endurance. When called upon to maximally perform, the diaphragm needs assistance.

That assistance is provided by the accessory respiratory muscles, primarily the intercostal muscles linking the ribs within the rib cage.

*The human diaphragm separating the lungs from the abdominal cavity. Graphic by John Clarke.*

Unless you’re reading this while running on a treadmill, your body is probably idling. Your heart is beating rhythmically, your diaphragm is methodically contracting and relaxing. But, if some dire event were to happen, you would be primed for action. If you needed to react to an emergency, your heart and lungs would race at full speed.

The difference between idling and full-speed capability is called physiological reserve, which in turn is divided into its components; cardiac, muscular, and ventilatory reserve. As drivers, pilots, and boat captains will attest, it’s always good to have fuel reserves. Likewise, physiological reserve is good to have in abundance.

The Dive

The following is an imaginary tale of a young, blond-haired hipster drawn to the Red Sea for a deep dive. He chose to dive on the wall at Ras Mohammed on the Eastern Shore of the Sinai, which descends quickly down to a thousand feet and beyond. That was his target—1,000 feet.

The previous year he bought a rebreather so gas usage should not be a problem for his deep dive. He also sprang for the cost of helium-oxygen diluent. Trimix would have been cheaper, but he spared no expense. Nothing but the best. To that end, he used loose-fill, fine grain Sodalime in his CO2 scrubber canister.

These were his thoughts as he descended.

Free-falling at three hundred feet. Never been this deep before. The water’s getting cold, so the warm gas from the canister feels good.

800 feet. Wow, the gas is thicker now.

When he reached the bottom, he realized something wasn’t right. He sucked harder and harder, feeling his full face mask collapsing around his face with each inhalation. He was “sucking rubber,” feeling like he was running out of gas, but his diluent pressure gage still read 1800 psi.

Unconsciously, he compensated for the respiratory load by slowing his breathing—easing his discomfort. Concerned, he briefly switched to open circuit bailout gas, but that didn’t feel any better. In fact, it was worse, so he switched back to the bag.

Surprisingly, he couldn’t get off the bottom. In fact, he was slipping further downslope. He needed to drop weights, but they were integrated. He fumbled with his vest, trying to remember how to release the weights, but he couldn’t work it out.

He found the pony bottle to inflate his integrated BC, but after a second’s spit of air, it stopped filling. He would have to swim off the bottom. As he struggled to swim upwards in the darkness, and without bubbles to guide him, he wasn’t sure which way was up.

His heart was beating at its maximum rate, trying to force blood through his lungs, but he couldn’t force enough gas in and out of his lungs to clear his bloodstream of its increasingly toxic CO2 load. The build-up of CO2 in the arterial blood was clouding his thinking. The CO₂ was making him want to breathe harder, but he couldn’t. The feeling of breathlessness—and impending doom—was overwhelming.

————

The accident investigation on the equipment was inconclusive. The dive computer had flooded, but that was irrelevant. Surface pre-dive checks were passed. The rebreather seemed to function normally when tested in a swimming pool. The investigators convinced a Navy laboratory to press the rebreather down to 1,000 feet, but nothing abnormal was found other than a slight elevation of controlled PO₂.

The Analysis

An asthma attack can kill by narrowing the airways in the lung, making the person suffering the attack feel like they’re sucking air through a clogged straw.

A healthy diver doesn’t have airways that constrict, but gas density increases with depth, causing the same effect as a narrowed airway. It becomes increasingly difficult to breathe as depth increases. A previous InDepth blog post on gas density discusses this subject.

Normal human airways compared to airways during an asthma attack. Graphic courtesy of Asthma and Allergy Foundation of America.

If the strength of respiratory muscles is finite, just as it is for all muscles, then any load placed on those muscles will eat away a diver’s “respiratory reserve.” From the diaphragm’s perspective, the total loading it encounters is divided between that internal to the diver and that external to the diver. As gas density increases, internal loading increases. A rebreather is external to the body, so flow resistance through a rebreather adds to the total load placed on the respiratory muscles. If the internal resistance load increases a lot, as it does at great depth, there is very little reserve left for external resistance, like that of a rebreather.

In this fictional tale of a hapless diver, he needlessly added respiratory resistance by using fine-grain Sodalime in his scrubber canister. Compared to large grain Sodalime, such as Sofnolime 408, fine-grain absorbent adds scrubber duration, but it also increases breathing resistance. It thus cut into the diver’s ventilatory reserve.

This fictional diver exceeded his physiological reserves by,

not understanding the effect of dense gas on the “work of breathing,”
not understanding the limitation of his respiratory muscles, and
by not realizing the “best” Sodalime for dive duration was not the best for breathing resistance.

He also didn’t realize that a rebreather scrubber might remove all CO2 from the expired gas passing through it, but it is ventilation (breathing) that eliminates the body’s CO₂ from the diver’s bloodstream. Once CO₂ intoxication begins, cognitive and muscular ability quickly decline to the point where self-rescue may be impossible.

Lessons from The U.S. Navy

Considering the seriousness of the topic, it is worthwhile to review the following figures prepared for the U.S. Navy.

First, we define peak-to-peak mouth pressure, a measure of the pressure exerted by a working diver breathing through the external resistance of a rebreather. Total respiratory resistance for a diver comes in two parts: internal and external. In the following figures, those resistances in the upper airways are symbolized by a small opening, and in the external breathing apparatus, by a long, narrow opening representing a UBA attached to the diver’s mouth.

*High external resistance. In this case, the difference between mouth pressure and ambient water pressure is called ΔP1* Credit with modifcation: “*Direct measurement of pressures involved in vocal exercises using semi-occluded vocal tracts”*.

*Low external resistance. The difference between mouth pressure and ambient water pressure is called ΔP2.* Credit with modification: “*Direct measurement of pressures involved in vocal exercises using semi-occluded vocal tracts”*.

*Mouth pressure waveforms ΔP1 and ΔP2 during breathing with high (P1) and low (P2) external resistance.*

This author reviewed over 250 dives by Navy divers at the Naval Medical Research Institute and the Navy Experimental Diving Unit. These were working dives involving strenuous exercise at simulated depths down to 1500 feet seawater, using gas mixtures ranging from air to nitrox and heliox. Gas densities ranged from about 1 gram per liter (g/L) (air at the surface) to over 8 g/L. Each dive was composed of a team of divers, so each plotted data point had more than one man-dive result included. An “eventful” dive was one where a diver stopped work due to loss of consciousness, or respiratory distress (“dyspnea” in medical terminology.) They were marked as red in the following figure. Uneventful dives were marked in black.

Using a statistical technique called maximum likelihood, the data revealed a sloping line marking a boundary between eventful and uneventful dives.

*Peak-to-peak mouth pressure and gas density conspire to increase a diver’s risk of an “event” during a dive.*

The fact that the zero-incidence line sloped downward illustrates the fact that the higher the gas density, the greater the respiratory load imposed on a diver by both internal and external (UBA) resistance. The higher that load, the lower the diver’s tolerance to high respiratory pressures.

By measuring peak-to-peak mouth pressures, we are witnessing the effect of UBA flow resistance at high workloads. It does not reveal the flow resistance internal to the body. However, when gas density increases, internal resistance must also increase.

The interrupted lines in the figure illustrate lines of estimated equal probability of an event. The higher the peak-to- peak pressure for a given gas density, the higher the probability of an eventful dive.

Figure 7 suggests that at a gas density of over 8 grams per liter, practical work would be impossible. The only way to make it possible would be to reduce gas density by substituting helium for nitrogen, or substituting hydrogen for helium, and then doing as little work as possible to keep ΔP low.

For our fictional 1,000 foot diver, the gas density would have been between 6 and 7 grams per L. Using a rebreather, there would be virtually no physiological reserve at the bottom. Moderate work against the high breathing resistance at depth would be very likely to result in an “eventful” dive.

Image Citation for medical graphics: Robieux C, Galant C, Lagier A, Legou T, Giovanni A. Direct measurement of pressures involved in vocal exercises using semi-occluded vocal tracts. Logoped Phoniatr Vocol. 2015 Oct;40(3):106-12. doi: 10.3109/14015439.2014.902496. Epub 2014 May 21. PMID: 24850270.

John Clarke, also known as John R. Clarke, Ph.D., is a Navy diving researcher in physiology and physical science. Clarke was an early graduate of the Navy’s Scientist in the Sea Program. During his forty-year government career, he conducted physiological research on numerous experimental saturation dives. Two dives were to a pressure equivalent to 1500 fsw.

For twenty- eight years he was the Scientific Director of the Navy Experimental Diving Unit.

Clarke has authored a technothriller-science fiction series called the Jason Parker Trilogy. All three volumes, Middle Waters, Triangle, and Atmosphere, feature saturation diving from depths of 100 feet to 2,500 feet. The deepest dives involve hydreliox, a mixture of helium, hydrogen and oxygen. UFOs, aliens, and an uncaring cosmos lay the framework for political and human intrigue both on and off-planet.

Although now retired, Clarke has worked for NEDU as a Scientist Emeritus. He now runs a consulting company, Clarke Life Support Consulting, LLC. He helps various companies, when he isn’t writing about diving, aviation, and space. His websites are www.johnclarkeonline.com and www.jasonparkertrilogy.com. His thriller series is available at Amazon and Barnes & Noble.

Related Blog Posts – Further Reading for Rebreather Divers

How Much is Too Much? (Carbon Dioxide – The Diver’s Nemesis)

Knock Yourself Out (Carbon Dioxide – The Diver’s Nemesis)

How Long Will Your Rebreather Scrubber Canister Last?

Does Your Rebreather Scrubber Operate in Its Goldilocks Zone?

A Look Inside Rebreather Scrubber Canisters, Part 1

Carbon Dioxide – The Diver’s Nemesis Pt. 1 (Meduna’s Mixture)

A Look Inside Rebreather Scrubber Canisters, Part 2

My Respiratory System is So Embarrassed

Hydrogen Diving: The Good, The Bad, the Ugly

In the preceding blog post, I reminded the reader that the Earth’s supply of helium is limited. It is not a renewable resource.

Being a diving professional, I am not concerned about the consequence of a helium shortage on party balloons. But I am thinking about the potential consequences on diving.

So, knowing that hydrogen has both good and bad traits, it would be prudent to begin thinking about whether or not there is a way to safely substitute hydrogen for helium in technical, scientific, commercial and military diving.

Perhaps the word “bad” is too much of an understatement. Perhaps “horrible” would be a better descriptor for something like the Hindenburg disaster.

With that sobering reminder of what can happen, we now cautiously move on to the science.

First, we begin with the explosion hazard of hydrogen in binary mixtures of hydrogen and oxygen.

For diving in the 10 to 20 bar range, 326 to 653 fsw range, the upper explosion limit is 94.2 molar percent. So that means that if a binary gas mixture contains 96% hydrogen and 4% oxygen, it should not explode when ignited.

Those underlined words are important. An explosive mixture of hydrogen and oxygen will not explode without an ignition source. Proof of that is exhibited in many college introductory chemistry lectures, and documented in the following YouTube video.

Arne Zetterström

As a forecast of our potential future, during World War II, Sweden was deprived of a ready source of helium coming from the U.S. and elsewhere. So, the clever and industrious Arne Zetterström conducted a series of experimental deep, hard hat dives from 1943 to 1945 using a mixture of 96% hydrogen and 4% oxygen on dives ranging from 12 to 17 bar.

Once at depth, Zetterström switched from a non-hydrox gas mixture to the “hydrox” gas mixture. His initial test dive was to 111 msw (362 fsw, 12 bar), progressing through six dives to a maximum depth of 160 msw (522 fsw, 17 bar).

That dive series was successful. Unfortunately, on the last dive on 7 August 1945, Zetterström died tragically when his dive tenders mistakenly pulled him directly to the surface from the bottom depth of 522 fsw. He died from fulminant decompression sickness.

From the above table we see that modern measurements confirm that Zetterström chose his gas mixes wisely. At a 96 mol% of hydrogen, he was above the upper explosion limit. If there had been an unexpected ignition event, his breathing gas mixture would not have exploded.

I have confirmed the oxygen partial pressure for Zetterström’s dives using PTC Mathcad Express 3.1 and will share the process.

First, I show pressure conversions familiar to Navy divers and diving scientists, but not known to most others.

For Zetterström’s 111 msw (362 fsw) dive, the partial pressure of oxygen (PO₂) would have been 0.478 atm, at the top end of the target range (0.4 to 0.48) for U.S. Navy chamber oxygen atmosphere during saturation diving. A PO₂of 0.48 is believed to be the highest PO₂ tolerated for extended periods. Saturation dives sometimes last over a month.

For Zetterström’s 6th and last dive, to 160 msw (522 fsw), the oxygen partial pressure was 0.7 ata, about half of what it normally is in modern electronic rebreathers with fixed PO₂.

A far more detailed story of the Zetterström Hydrox dive series can be found in this book.

Arne Zetterström Memorial Dive

In 2012, the Swedish Historical Diving Society and the Royal Institute of Technology (KTH) Diving Club, Stockholm, conducted an Arne Zetterström Memorial dive to a relatively shallow depth of 40 msw or 131 fsw. The original 96% – 4% ratio of hydrogen and oxygen was maintained, resulting in a gas mixture with a PO2 of 0.20 atm.

As reported in the KTH Dive Club’s Dykloggen (dive log) report of July 2012, the team lead was Ola Lindh, Project Leader and Diver. Åke Larsson, another diver, contributed the following information about that dive.

The Hydrox divers used open circuit scuba, with back mounted air, and for decompression, bottles of hydrox and oxygen.

The Swedish divers did not go deeper than 131 feet because they were just above the mud at that depth in a quarry. Plus, they did not yet have details of Zetterström’s decompression plan for deeper diving.

Today, they do possess the wartime hydrogen decompression plan, so deeper hydrogen dives may be forthcoming.

Three gas mixtures – hydrogen, and air (nitrogen and oxygen)

When you mix an inert gas like nitrogen (or perhaps helium?) with hydrogen and oxygen mixtures, that greatly reduces the explosion hazard. But as this video shows, sooner or later the ratios might change enough to become explosive.

Naval Medical Research Institute

I spent 12 years working as a diving biomedical researcher at the Naval Medical Research Institute (NMRI) in Bethesda, MD.

Main entrance to the Albert R. Behnke Diving Medicine Research Center, at NMRI.

My laboratory was in the Behnke Diving Medicine Research Center building, but the hyperbaric hydrogen facility was situated a safe distance behind the main building. In the unlikely event of an explosion, the main Behnke facility and its hyperbaric chamber complex would be preserved.

The hyperbaric hydrogen facility was used to test the effects of high-pressure hydrogen and biochemical decompression on pigs, rather than risk human divers. And all of that was done safely, thanks to the professionalism of Navy divers and scientists.

Dr. Susan Kayar checking on the hydrogen diving pigs.

Kayar, a member of the Women Divers Hall of Fame, used at 230 msw (751 fsw) a gas mixture of 88% hydrogen, 2% oxygen, balance helium with a slight amount of nitrogen. That 88% hydrogen mixture put the gas mixture well above the 71.3% upper explosion limit for three gas components at 24 bar pressure. The resulting PO2 was 0.5 ata.

Compagnie Maritime d’Expertises (COMEX)

COMEX and their human-rated hyperbaric chambers are located in Marseilles, France.

When it came to manned hydrogen diving, the effect of hydrogen narcosis forced COMEX to operate below the upper explosion limit during its long series of experimental hydrogen dives.

In 1985, COMEX’s Hydra V was the first manned hydrogen dive to 450 msw. Hydrogen fraction was 54%, helium fraction was 45%, and oxygen fraction 1%. PO₂ was a nominal 0.45 atm, the same partial pressure used by the U.S. Navy for saturation dives.

In 1988 during Hydra VIII, the first open water hydrogen dive, the depth was 534 msw, or 1752 fsw. Hydrogen fraction was 49%, helium fraction was 50%, and oxygen fraction 1%. The resulting oxygen partial pressure was 0.54 atmospheres.

The following video documents the record-breaking Hydra VIII dive.

The 534 msw Hydra VIII depth record was broken by Hydra X, a 701 msw, 2300 fsw chamber dive. The gas mixture was the same as in Hydra VIII, hydrogen fraction 49%, helium 50%, and oxygen percentage 1%. Due to the increase in depth, PO₂ rose to 0.7 atm, an oxygen partial pressure frequently used in older U.S. Navy rebreathers.

The head of the Diving Medicine Department at NMRI, CAPT Ed Flynn, M.D. (glasses and grey hair sitting on the right side of the console), was performing physiological studies on both Hydra VI and VIII. In essence he was the Patron Saint of the NMRI Hydrogen Research Facility.

Shallow Hydrogen Diving

What have the previous studies taught us? Well, for one thing, the Swedes showed in their Arne Zetterström Memorial dive that you can get away with oxygen concentrations close to normoxia, PO₂~0.21 ata. The disadvantage of normal atmospheric partial pressures of oxygen, compared to higher pressures, is related to decompression time. There is a decompression advantage when breathing oxygen pressures of 1.3 to 1.45 ata. Virtually all modern electronic rebreathers use those oxygen pressures for that reason. But as the KTH Dive Club showed, hydrogen decompression can be safely handled at relatively shallow depths.

For recreational divers, there is an economic advantage for reducing helium usage by substituting nitrogen. We don’t yet know what the economic and safety comparison would be when using helium diluted hydrogen versus pure hydrogen.

Hydrogen, helium, and oxygen were the standard gases used by COMEX. But they were likely chosen to lessen hydrogen toxicity. Hydrogen toxicity would not be a problem at shallow depth. And in fact, the KTH Dive Club reported no toxicity problems.

Retrospection

As proud as I have been of the record-breaking COMEX hydrogen research program, and of the highly imaginative U.S. Navy hydrogen research program, it has not been lost on me that the first deep human hydrogen dives were conducted by an undoubtedly low-cost program led by a single Swedish Naval Officer, Arne Zetterström.

Now, I find it remarkable that the people testing hydrogen diving at relatively shallow depths, would also be Swedish. Unlike the COMEX and NMRI projects described above, I suspect the KTH Dive club was not sponsored by multimillion dollar programs.

You have to admire the Swedish chutzpah.

Disclaimer: The author is no longer employed by the Navy or Department of Defense. All opinions are my own, and not those of any government agency. This document is posted purely for historical and educational interest. At risk of violent death, under no circumstances should the reader be tempted to explore the production, storage, or use of hydrogen without thorough and certified safety training.

What Will Divers Do When the Helium is Gone?

Helium is a low density, non-narcotic gas often added to the breathing gas mixture of divers who have to dive deep. Nitrogen, the primary component of air is both dense, making it hard to breathe when diving deep, and narcotic at depths below one hundred feet. That is why nitrogen leads to the so-called “rapture of the deep.” Narcotic divers make bad decisions.

If it weren’t for helium, some of the deepest and most sensitive diving for national security would never have happened. So, it’s really important. Commercial saturation diving in the oil fields of the North Atlantic and the Gulf of Mexico is wholly dependent on the easy to breathe and non-narcotic properties of helium.

Both civilian and government science divers, technical divers, and underwater cave explorers have been able to extend their diving range and safety because of helium in their breathing gas.

Helium graphic from the cover of a 2016 report on helium supply shortages by the American Physical Society, the American Chemical Society, and the Materials Research Society. — Image credit – Ashley Mumford

For those not familiar with the second lightest gas in the periodic table, I’ve included a Fast Fact from the Bureau of Land Management (BLM) at the end of this post.

There are two drawbacks to helium. A source of breathable helium is sometimes hard to locate, and the gas is expensive. Because of that expense and growing scarcity, it is forecast to become increasingly difficult to find, especially in remote locations.

From a Science Direct article, “Ongoing ascent to the helium production plateau – Insights from System Dynamics” in Resources Policy, Vol. 35, Issue 2, June 2010, pgs 77-89.

The primary source of helium, a non-renewable resource, is from gas wells. As shown in the BLM summary at the bottom of this post, the demand for helium is high in scientific, medical, military, and commercial applications.

Cryomodules for an x-ray light source LCLS-II are under construction at Fermilab in Illinois. The cryomodules will house superconducting cavities that are cooled with liquid helium. Credit: Reidar Hahn.

Not on the list, and the least likely to be considered during allocation of an increasingly scarce resource, is civilian diving, and perhaps even military diving.

The above graphical projection made in 2010 does not consider the damping effect of current government policies which make drilling oil and gas wells, and fossil fuels in general, undesirable. While Qatar and Russia have significant helium reserves, helium transported from distant countries will come with a much higher price tag than forecast in 2010. Unfortunately, no one has so far calculated the net cost of reducing the recovery of gas from the ground, and the recovery of the helium contained in that natural gas.

Why might the next century bring a lowering of helium prices as predicted in the graph above? As I’ve explained in Atmosphere, Book 3 of the Jason Parker Trilogy, fusion reactors should hopefully be common place by then, and helium is a byproduct of those fusion reactions. Of course, the above graph reflects a great deal of uncertainty about the next century, even without the uncertainty introduced by government policies. But our immediate concern is this century, not the next.

One approach to helium conservation is by using rebreathers to conserve gas rather than exhaust it into the water column, as is done in open circuit diving like that pictured in the first underwater photo with two Navy divers. In rebreathers, the only helium wasted is that used to keep breathing bags inflated on descent. Unfortunately, that gas is “burped-off” as gas expands on ascent. But the amount of inert gas wasted during rebreather operations is still far less than in open-circuit diving.

A Navy EX-19 rebreather being tested in Morrison Springs, FL. Navy photo by Bernie Campoli.

Another option for holding down helium cost, is to use helium in “Trimix”, a mixture of oxygen, nitrogen and helium. Such mixes become popular for use at depths of 200 feet sea water (fsw) and deeper. It minimizes the cost of helium while simultaneously reducing the effect of nitrogen narcosis.

A common trimix is called 21/35, which has 21 percent oxygen, 35 percent helium and 44 percent nitrogen. Another common mixture is 18/45, with 18 percent oxygen and 45 percent helium. Those helium percentages are considerably reduced from that found in a typical military heliox mixture containing no nitrogen.

But even then, using helium for recreational deep diving may become far too expensive for any but the richest recreational divers. Already, it’s reported that scientific and medical instruments like superconducting magnets and MRI machines have been affected by helium shortages.

Here are some relevant links from Science Direct and the American Institute of Physics.

When it comes to the DoD prioritization of military saturation diving missions compared to other military options, the availability and cost of helium will inevitability factor into the high-level decision tree.

So, is there an alternative to helium use in diving? Well, yes and no. I’ve written in both this blog and in my novels about the use of hydrogen in diving, as has a biomedical researcher friend of mine, Susan Kayar, Ph.D. in her novel, Operation Second Starfish.

Hydrogen is even lighter than helium, but at great depth it is narcotic. One strange thing about hydrogen narcosis is that at great depth it can result in psychotic manifestations in some individuals. Also, at shallow depth, hydrogen can form an explosive mixture with oxygen, an issue I’ll discuss in my next post. So, it has to be used with great care and attention to details.

Interestingly, the math says that at 200 fsw, the depth where trimix is typically used, hydrogen can be safely substituted for helium. However, only experimentation can prove if that prediction is valid or not. But as helium gets scarcer and more expensive, using hydrogen in place of helium is something worth considering.

[DO NOT CONDUCT YOUR OWN EXPERIMENTS WITH HYDROGEN. THERE IS ALWAYS A CHANCE OF INJURY OR DEATH WITH HYDROGEN. THINK OF THE HINDENBURG!]

Below are links to other hydrogen and forward-looking diving posts in this blog.

Hydrogen Diving – A Very Good Year for Fiction

Diving with Hydrogen – It’s a Gas

Back to the Future – from a 2000 Discover Issue

Helium Fast Facts

Fact Sheet—BLM New Mexico Amarillo Field Office

Helium: Questions and Answers

What is helium?

Helium is an odorless, colorless, and tasteless gas. Helium, more than 99.9 percent pure, is also used in liquid form at -452 degrees Fahrenheit.

Where does helium come from?

Helium occurs with other gasses in pockets beneath the Earth’s surface. The most economical source of helium is natural gas, all of which contains some helium. Natural gas in the States of Texas, Kansas, Colorado, Utah, and Wyoming is richer in helium than what has been recovered from other States.

How is helium produced?

When a gas pocket containing economically recoverable amounts of helium is found, a well is drilled to release the gas. It travels by pipeline to a processing plant where the helium is separated from the other gasses. One method of separation is a cryogenic process, which uses cold temperature differences to split the components. Another process, membrane filtration, uses molecular size difference to split components.

What is helium used for?

Today, helium plays a prominent role in medical imaging (magnetic resonance imaging), fiber optics/semiconductor manufacturing, laser welding, leak detection, superconductivity development, aerospace, defense, and energy programs.

Is helium renewable (does it naturally replenish itself after humans use it)?

No, helium is a non-renewable resource. That is why the Federal Government stored 44 billion cubic feet of helium in a natural gas reservoir at Cliffside, just outside of Amarillo, Texas. Helium was injected into porous rock 3,000 feet below the Earth’s surface during the 1960s. This rock holds gas like a sponge holds water. Two layers of calcium anhydrite cover the rock, acting as a lid. The sides are surrounded by water.

Bubble Submarines Resurface After Fifty-Two Years

A December, 2019 article in the New York Times has the catchy headline, “Bubble Subs Arise, Opening Eyes to the Deep Sea.”

From my perspective, it’s always great when anything about the deep sea attracts the attention of major newspapers. In general, well researched and written publications on the subject are hard to find. A happy exception is biologist Bill Streever’s latest book, In Oceans Deep.

Streever’s excellent book has much to say about free diving, Navy diving, and even one-atmosphere diving suits (wearable submarines, if you will.)

But back to the NYT. William Broad’s article on mini-submarines is both colorful and informative. I urge you to read it if you have even the slightest interest in the undersea world.

However, just as the title of this blog post is deliberately hyperbolic, tongue in cheek, the NYT article is a bit misleading. Just because the technology may be new to the New York Times, it doesn’t mean it’s truly new. Bubble Subs have not actually risen of late. They, and the concepts behind them, have been around for a long time.

To prove my point, this blog post republishes the most interesting parts of an article I penned in the Georgia Tech Engineer way back in 1967. It’s called The Depth Challenger. The article is a little technical, which is the norm for an engineering school magazine, but it was also written to appeal to a diverse student body.

Artist’s conception of a 56-in diameter sphere mounted on its 16-foot maneuvering sled.

The article begins with a short piece of descriptive prose.

A brittle star, its arms twitching, spreading across the firm, grey mud, stops as a tracking light sweeps over and beyond it. An instant later the light returns and fixes on the animal as the whirring bubble slides in close overhead. The sphere hovers briefly then moves off, circling, finally disappearing below a canyon rim. When minutes later the bubble settles to rest on the soft canyon floor, cameras clicking, the two men inside sit gazing, peering, with four miles of water above their heads. These men are new frontiersmen – the oceanographers.

One of the greatest problems preventing our full utilization of the ocean’s potential is the inability of re search devices to withstand the enormous pressures exerted by deep water. At four thousand feet, the sea exerts one ton of pressure on each square inch of surface. At thirty-five thousand feet, the pressure is more than seven and a half tons per square inch. To date, nothing has been developed with the ideal requirements of 1) withstanding deep sea pressure, 2) containing man for extended periods of time, and 3) enabling direct visual observation. However, a solution to these problems may soon be met by glass submarines. H. A. Perry, research materials engineer at the Naval Ordnance Laboratory of Silver Springs, Maryland, is currently researching the feasibility of transparent submarine hulls. Perry states that glass provides a unique degree of buoyancy and safety in deep submergence hulls.

To test his original hypothesis, Perry and other NOL scientists set sail in 1964 aboard the Navy research vessel Gillis with a cargo of 95 hollow spheres provided by Corning Glass Works and the Pittsburgh Plate Glass Company. Once over the Puerto Rico trench, these spheres were lowered to depths of 300, 7000, 1400 and 2100 feet. Pentolite-charges were set a fixed distance away and detonated. If no leakage of the sphere occurred, the charges were moved closer until the glass finally failed. At this point, a “critical distance” was defined. As depth increased, the compressive strength of the glass also increased. With metal hulls, the results are just the opposite.

(As a side note, a few years later I set sail on the same vessel, by then renamed the RV Gillis, for a research cruise to the Puerto Rico Trench.)

Apparently, the deeper a glass submarine dives, the safer are its occupants; that is, down to an optimum depth of about 21,000 feet where the compressive strength diminishes until buckling finally occurs at a theoretical depth of 55,000 feet. However, the deepest part of the ocean, the Challenger Deep, is a trench descending to only 35,888 feet, so the theoretical limit for glass spheres poses no problem. It will be noted, though, that the compressive strength of conventional spheres at relatively low pressures is in itself rather low. The chances of a mariner surviving an accidental collision on down to a depth of several hundred feet is nil. Obviously, there is a need for either foolhardy scientists or “pre-compressed hulls.”

The full article with illustrations can be read here.

Bubble-Sub-1

In my opinion, the epitome of bubble submarines has been the Johnson Sea Link, pictured here. This revolutionary bubble submarine started operations in 1971, with upgrades in 1972, just a few years after I got wind of it.

Ocean on Top

When I was a graduate student, I found Hal Clement’s science fiction novel in the Florida State University Bookstore. I had just completed a summer in the U.S. Navy-sponsored Scientist in the Sea Program in Panama City, Florida. Being an avid diver, and a burgeoning scientist, my imagination was captured by Clement’s book.

I read his book shortly after it was published in 1973, but after graduating and moving, I lost the book. Unfortunately, I also forgot the book’s title and the author’s name. Yet I still felt a deep connection with the story, and for that reason, I spent decades looking for it, without success.

Recently, my luck changed. While browsing the Wikipedia topic on liquid breathing, I found the source I had long been searching for. “Hal Clement’s 1973 novel Ocean on Top portrays a small underwater civilization living in a ‘bubble’ of oxygenated fluid denser than seawater.”

There it was, at last. And best of all, that bubble turned out to be perfluorocarbon, an exotic, heavier than water, transparent liquid. In reality, filling a person’s lungs with it, is not as murderous as it would seem.

I was ecstatic: could this really be the book I’d been seeking for decades? Being on travel at the time, I searched for an Audible version of the book. Again, I was in luck: there was a version narrated by Tom Picasso. (Thank-you, Wikipedia and Audible, for providing instant gratification!)

With a bit more research, I discovered that “Hal Clement” was the pen name for Harry Clement Stubbs. I ordered two copies of his first edition, one of them signed with both his pen name and real name.

Harry (Hal) Stubbs passed away at age 81, in 2003. Born in 1922, Stubbs was an early leader in the “hard science fiction” genre, where science fiction is infused with scientific facts and logic.

The original version of his story was a Magazine serial version, copyrighted in 1967 by Galaxy Publishing Corp., for Worlds of If.

While the publication of the 1973 book version of Clement’s story might have been influenced by the Energy Crisis of 1973, , the date of the original publication, 1967, suggests that Clement was simply prescient. I would be surprised if in the 1960s, a science fiction writer of ordinary skill could have envisioned the global Energy Crisis of 1979.

Yet, here it is, the publisher’s summary of Ocean on Top: “Aquatic Enigma – The world’s energy was limited… and with overpopulation and a high level of technology, the Power Board had virtually become the real government of the world. Power was rationed, it was guarded, it was sacred. Thus, when three of the Power Board’s agents disappeared at sea, and there was evidence that something irregular was happening to the energy quota in that area, it was cause for real alarm.”

In 1979, while I was stuck in long lines waiting for gas in Maryland and Washington D.C., I vividly remembered the premise behind the book whose title evaded me. What a curious prediction that author had made, a prediction that in part had come true.

Of greater interest to me in 1973, as a newly fledged Navy-trained science diver, was the book’s prediction of the consequences of contemporaneous U.S. Navy-funded work on liquid breathing by human divers. In the 1970s, Johannes A. Kylstra was the primary researcher working on that project in the hyperbaric laboratory at Duke University.

Some critics say Ocean on Top was not the best of Clement’s works. Arguably, that honor belongs to his earlier Mission of Gravity(1954). However, if you are curious about the prospects of forsaking the land and living under the sea, his 1973 book raises some interesting points. One is that it posits the divergence of humans into two races; air-breathing humans and liquid breathing humans.

It also predicts, convincingly, some of the communication difficulties such a human divergence would cause. After all, our anatomical speech apparatus is designed for working in air, not fluid.

Perhaps it was the subliminal memory of Clement’s little book that influenced the storyline in the recent work, Atmosphere, Book Three of the Jason Parker Trilogy. After all, liquid breathing was an exciting science and science fiction concept back in the day, and surely worth a resurgence in this century, based on modern science.

I say “modern science” for two reasons: the first is because liquid perfluorocarbon is now instilled in lungs for medical treatment. Secondly, thanks to new molecular engineering technology like CRISPR-Cas9, we now foresee how genetic engineering can potentially lead to a divergence of the human species.

If Hal Clement was still around, I have no doubt he’d be writing many more science fiction novels about a future that just might be more realistic, and with more immediacy, than we think.

Hydrogen Diving – A Very Good Year for Fiction

It is incredibly unlikely that two scientist colleagues, Susan Kayar and myself, separated by large amounts of time and distance, would independently publish two novels about deep hydrogen saturation diving, in the same year. Unlikely or not, it happened in 2017. Neither author was aware of the other’s intentions, or even their whereabouts.

Some things are inexplicable.

Hydrogen diving is, to use an over-used analogy, a double edged sword. On the one hand it makes truly deep diving possible, yet it can cause bizarre mental effects on some deep hydrogen divers. And that dichotomy is grist for any novelist’s mill.

I had previously written about hydrogen diving and the pioneering role a Swede named Arne Zetterström had in developing it. Unfortunately, perhaps because he was a bold diver, he did not survive to become an old diver. Ironically, his death while diving wasn’t the fault of the hydrogen, but of his inattentive tenders. But as they say, that’s another story.

Once the remarkable, serendipitous co-publication of these two hydrogen diving novels became known, Kayar and I decided to post reviews, each about the other’s book. After all, if we didn’t, no one else would.

Quoting from Dr. Kayar’s biography listed on her Goodreads site, “Susan R. Kayar holds a doctorate in biology from the University of Miami. Her research career in comparative respiratory physiology spanned more than twenty years. She was the head of a research project in hydrogen diving and hydrogen biochemical decompression in animal models at the Naval Medical Research Institute, Bethesda, Maryland. She currently resides in Santa Fe, New Mexico, with her husband Erich; they met when they were both performing research at NMRI. Dr. Kayar was inducted into the Women Divers Hall of Fame in 2001 for her contributions to the study of diving physiology and decompression sickness.”

As for me, my bio is included in the About page of this blog.

My review of her book, Operation SECOND STARFISH: A Tale of Submarine Rescue, Science, and Friendship, is repeated here, and her review of mine is at the bottom of this post.

“Submarine deep sea “black ops” can be risky business even when everything goes well. But when things go badly, submariners’ lives are in peril, and everyone is praying for a miracle, and a savior. This well written novel drops you into the middle of such a desperate situation, and the potential savior, or potential scapegoat, is an unexpected protagonist, a female civilian scientist who knows the Navy way, knows how to motivate Navy divers, and unconsciously toys with their affections. This is a sensitively written account with a focus as much on interpersonal relations as on the technical aspects of hydrogen diving and biological decompression, or “Biodec.” Some of the greatest themes in this story are of the personal heroism of divers willing to risk their lives in the cold, foreboding darkness of the deep sea in an improbable effort to save fellow sailors.

The story may be fictional, but the science is not. In fact, for all the reader knows, everything written could have happened, or perhaps will, the next time the Navy has a submarine stranded on the bottom. The author, Susan Kayar, Ph.D. has pursued with Navy funding the very technology exposed in this story.

Amazingly, this is one of two novels published independently by scientists in the same year concerning record breaking deep hydrogen dives conducted on super-secret national security missions. That is a rare coincidence indeed, since to my knowledge no other novels about deep hydrogen diving have ever been written.

The other book is a sci fi techno-thriller called Triangle: A Novel, the second volume of a trilogy published by one of Kayar’s fellow scientists and colleagues, this reviewer. In both books, the hazards of deep diving are very real, and the tension is palpable. If you want to learn of the possibilities and perils of deep hydrogen diving, and experience the heroism of exceptional men and women in extraordinary circumstances, you now have two books to both entertain and painlessly inform you.

Kayar’s book will leave you wishing you could ride along with Doc Stella as she rides off into the sunset on her Indian motorcycle. What a ride it is.”

Kayar’s review of my novel, Triangle, the second in the Jason Parker Series of science fiction thrillers, follows.

“I thoroughly enjoyed Triangle, the second novel in the Jason Parker Trilogy by John Clarke. It is a fun and engaging mash-up of diving science and science fiction. John and I worked together in diving research for the Navy in Maryland years ago. He continues to this day to perform diving research for the Navy in Florida (while I moved on to other activities and then retired). As one would expect, his details in diving science and Navy jargon are impeccable. But it is impressive that his characters are well drawn and his plot twists are creative and bold.

My favorite part of Triangle has to be the ultra-deep hydrogen dive sequence for admittedly personal reasons. John and I, friendly colleagues though we were, had not been in contact with each other for a couple of decades or more. And yet my own diving novel, Operation SECOND STARFISH, was published in the same year as Triangle, and also contains an ultra-deep hydrogen dive sequence. Mutual friends had to tell us that the other had published a book for us to re-establish contact. I would imagine that our two books are the only novels ever to describe a hydrogen dive, which is a huge technical and physiological challenge, as readers will discover. John’s hydrogen dive works out (if I dare say so without revealing too much of his excellent plot) about as well as such a dangerous scenario ever will. My hydrogen dive is a lot rougher, in keeping with the more aggressive compression rate chosen to respond to the disabled submarine rescue that forms the basis of my story.

Any readers truly interested in dives well beyond 1000 feet of seawater will find a lot to learn and marvel over in Triangle. Readers just along for the exciting sci-fi ride will be equally happy to have spent time in John Clarke’s imaginative world. I look forward to his predicted December release of the third novel in this series.”

Anyway you look at it, these two fun novels contain a cram course in the rarest type of diving there is, diving with hydrogen as a breathing gas.