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.

Click photo to go to the Amazon page.

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.

Click photo to link to the NYT article.

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.

Harry Clement Stubbs, aka Hal Clement.

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

First publication.

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.

Promo image for the movie, Aquaman.

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.

Cover for the second edition.

Hydrogen Diving – A Very Good Year for Fiction

Susan R. Kayar

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.

 

Dead Space – A Lesson in Survival

Dead Space is a defunct, or shall we simply say “dead,” survival horror game that enthralled computer game players from 2008 to at least 2013. Sadly, the company that designed the horrifically beautiful game, Visceral Games, is no more. It has been, so to speak, eviscerated.

The main protagonist of the Dead Space Series was Isaac Clarke. If I was a game player I think I would be an Isaac fan since he was one of those rare Clarke’s known as a “corpse-slaying badass.” If in some unforeseen future my survival depended on being such a slayer, I’d want to be badass about it too, just like Isaac. As they say, anything worth doing …

Isaac Clarke and his Dead Space world make a great segue to introduce another matter of personal survival. And that is DEAD SPACE in underwater breathing equipment.

Clarke has proven to be equally at home underwater and in space due to his interesting cyan-lighted helmet. (I’m not sure where his eyes are, but perhaps in the 26th century a multi-frequency sensor suite makes a simple pair of eyes redundant.)

Historically, the U.S Navy used the venerable MK 5 diving helmet and the MK 12 diving helmet, which although they had no sensor suites, at least allowed divers to work at fairly great depths without drowning. However, they shared a common problem: Dead Space.

In ventilation terms, dead space is a gas volume that impedes the transfer of carbon dioxide (CO2) from a diver or snorkeler’s breath. When we exhale through any breathing device, hose, tube, or one-way valve we expect that exhaled breath to be removed completely, not hanging around to be re-inhaled with the next breath.

But a diving helmet inevitably has a large dead space. The only way to flush out the exhaled CO2 is by flowing a great deal of fresh gas through that helmet. A flow of up to six cubic feet of gas per minute is sometimes needed to mix and remove the diver’s exhaled breath from a diving helmet like the MK 12.

In more modern helmets, the dead space has been reduced by having the diver wear an oral-nasal mask inside the diving helmet, and giving the diver gas only on inhalation using a demand regulator like that used in scuba diving. The famous series of Kirby Morgan helmets, arguably the most popular in the world, is an example of such modern helmets.

Full face masks are used when light weight and agility is required, as in public service diving, cold water diving, or in Special Forces operations. The design of full face masks (FFM) has evolved through the years to favor small dead space, for all the reasons explained above.

 

Erich C. Frandrup’s 2003  Master’s Thesis for Duke’s Department of Mechanical Engineering and Materials Science reported on research on a simple breathing apparatus, snorkels. You can’t get much simpler than that.

Frandrup confirmed quantitatively what many of us knew qualitatively. Snorkels are by design low breathing resistance, and low dead space devices. Happily, the dead space can be easily calculated, as simply the volume contained within the snorkel.

Surprisingly, some snorkel manufacturers have recently sought to improve upon a great thing by modifying snorkels, combining them with a full face mask. The Navy has not studied those modified snorkels since Navy divers don’t use snorkels. However, you don’t get something for nothing. If you add a full face mask to a snorkel, dead space has to increase, even when using an oral-nasal mask.

So what?

In 1995 Dan Warkander and Claus Lundgren compared the dead space of common diving equipment, including full face masks, and reported on increases both in diver ventilation and the maximum amount of CO2 in the diver’s lungs. Basically the physiological effects of dead space goes like this: we naturally produce CO2 during the process of “burning” fuel, just like a car engine does. (Of course our fuel is glucose, not gasoline.) The more we work, the more CO2 we produce in our blood, and the more we have to breathe (ventilate) to expel that CO2 out of our bodies.

If we are exhaling into a dead space, some of that exhaled CO2 will be inhaled into our lungs during our next breath. That’s not good, because now we have to breathe harder to expel both the produced CO2 and the reinhaled CO2. In other words, dead space makes us breathe harder.

Now, if we’re breathing through an underwater breathing apparatus, hard breathing is, well, hard. As a result, we tend to get a little lazy and allow CO2 to build up in the blood stream. And if that CO2 get high enough, it’s lights out for us. Underwater, the lights are likely to stay out.

In a computer game like Dead Space, no one worries about helmet dead space. But if a movie is ever based on the game, whichever actor plays Isaac Clarke should be very concerned about the most insidious type of Dead Space, that in his futuristic helmet. It can be (need I say it?) — deadly.

 

 

 

 

 

 

 

 

 

If I Had Written the Score to Interstellar

If I was Hans Zimmer, I would be a bit annoyed.

What is arguably the best score Hans Zimmer has ever written, the music for Interstellar, has thrilled me to my core. However, I came to that conclusion by an indirect route.

Like many of you, I saw the movie in all it’s cinematic glory when it was released in 2014. But it was not until 2017 that I fell in love with it, both the movie and the score.

In preparation for an after-dinner talk to a panel of the American Heart Association’s 2017 Science Conference, I was looking for an inspirational way, preferably with great video and sound, to describe the sport of competitive free diving. This past summer I had the opportunity to meet some of the world’s best free divers and free diving instructors in a Colloquium put together by the University of California at San Diego, Center of Excellence in Scientific Diving.

I had pretty much given up on finding something to help me illustrate the beauty, and challenges, of competitive free diving. That changed, however,  when I came across a posting from a group of tactical military divers. In a short 3-minute video the young French diver Arnaud Jerald set his personal free diving (CWT, Constant Weight Dive  discipline) record of 92 meters in a competition in Turkey. He placed third in a field which included world record holders in the same event.

Three things made the diving video great, in my opinion: 1) the subject matter which vividly shows a human activity little known by most people, and understood by even fewer; 2) steady and clear video produced by a new underwater camera, the Diveye, and 3) the accompanying music.

A film score is only successful if it aids the audience in generating an emotional response to a movie scene. In that respect, a great movie hinges not only on good acting and script, but on an almost telepathic connection between the film director/producer and music director/composer.

In the free diving video clip, the accompanying music swelled in concert with the audience’s tension, generated perhaps unconsciously in response to the drama of the moment. And then there was organ music at just the right point. For me a pipe organ truly is the most impressive and grand of any musical instrument.

And just when the cinematic moment was right,  you could hear the heart beats, helping us realize what a strain it must have been on young Jerald’s heart as he reached his deepest depth, far from the surface, and air.

Indeed, when I gave the presentation, the video clip seemed to have the effect on the audience that I was looking for. But afterwards, I was relieved that no one had asked me where that music came from. I had no idea.

I don’t recall what led me to Interstellar as the music source: it may have been a random playing of movie soundtracks on a music streaming service, but once I heard a snippet, I recognized it. “That’s it!” I shouted to no one in particular.

It wasn’t just me; my family, including a nine-year old granddaughter had heard me rehearse my talk many times, and they also immediately recognized the similarity between the free diving video, and part of the Interstellar soundtrack.

The closest musical correlation to the diving video was the “Mountains” track in the movie soundtrack. Strangely, the match was not perfect. In fact the differences were easily notable, a fact I discovered after I bought both the movie and the Hans Zimmer soundtrack. And I must note, I think the music in the diving video is better.

Perhaps the full music was present in the original version of the movie, and perhaps some fancy mixing in the sound room deleted it. If so, too bad. But I must admit, the quiet musical nuances would have been missed during the cacophonous sound of a 4000 foot tall tidal wave sweeping upon a tiny spacecraft. There was lots of shouting and screaming.

As for my opinion that Hans Zimmer might be annoyed, well, I suggest you watch the portion of the full movie where the Mountain track rises to prominence. That is the part where the tidal wave, initially mistaken as mountains, appears on the horizon of the first planet the Horizon space craft landed on outside of our galaxy.

As exciting as the action was, and as wonderfully crafted the dialog and acting, it obscured the finer points of the music. Fortunately, the free diving video, coming as it does with no dialog at all, puts the music in the perspective that I, at least, can completely enjoy.

I find it fitting that in both videos, the incredibly powerful music was used to showcase humans extending themselves to their absolute limits. Of course, one of those stories is fictional, and the other is real.

 

 

 

A Matter of Chance: Music Makes the Video

I was recently asked to give a 30-minute after-dinner talk to the 3CPR Resuscitation Panel of the American Heart Association at their annual scientific meeting in Anaheim, CA. In the audience were scientists, cardiologists, anesthesiologists, anesthetists, emergency physicians, and resuscitation technicians. It was a multimedia event with professionally managed sound and video.

Knowing that the group would be well acquainted with the role of chance in medical procedures, I chose to use a segue from medicine into the topic of extreme adventures in military and civilian diving. The focus of the talk was on how chance can turn adventures into mis-adventures.

I revealed three areas where Navy Biomedical Research is expanding the boundaries of the state of the art in military and civilian diving. One area was in deep saturation diving, another was polar ice diving, and the third was breath hold diving.

As an introduction to polar diving, I wanted to create a video travelogue of my National Science Foundation-sponsored research and teaching trips to the Arctic (Svalbard) and Antarctica (McMurdo Station and vicinity.) These projects were spearheaded by the Smithsonian Institution, and my participation was funded in part by the U.S. Navy.

To begin the preparation of the video, I assembled my most relevant photos, and those taken by various team mates, and imported them into my favorite video editing software, which happens to be Cyberlink Director.

Then I went looking for potential sound tracks for the approximately 5 minute video. Considering the topic, I thought Disney’s Frozen would have familiar themes that might be acceptable. I rejected a number of YouTube videos of music from Frozen; most were too close to the original and included vocal tracks. Finally I came across the “Let It Go Orchestral Suite” composed by the “Twin Composers,” Andrew and Jared DePolo.

It was perfect for my application. I extracted the audio track from the Suite as shown on YouTube, imported it into Director, and lined it up with the nascent video track which included all images and other video segments.

To match the music to the video, I simply cut back on the duration for each of 97 images, keeping the other 5 videos in their native length. By experimentation, I found that 3.21 seconds per image resulted in the last image fading out as the music came to a close and the end credits began to roll.

On the first run through of the new video, I couldn’t find anything to complain about; which for me is rare. So I ran it again and again, eventually creating an mp4 file which would play on a large screen and home audio system. But I couldn’t help notice that the gorgeous score would sweeten at interesting times, and serendipitously change its musical theme just as the video subject matter was changing.

How fortunate, I thought. It was then that I began to realize that “chance” had worked its way into the production effort, in an unexpected way.

First, the music seemed to my ear to be written in 4/4 time, with each measure lasting 3.2 seconds, precisely, and purely by happenstance matching the image change rate. At a resulting 0.8 seconds per beat, or 75 beats per minute, that placed the sensed tempo in the adagietto range, which seemed appropriate for the theme of the music. (Without seeing the score, I’m just guessing about the tempo and timing. But that’s how it felt to me.)

The timing coincidence was rather subtle at first, but as the finale began building at the 3:39 minute mark, the force of the down beat for each measure became more notable, and the coincidence with image changes became more remarkable. There was absolutely nothing I could do to improve it.

In some cases the technical dissection of music can be a distraction from the beauty of the music, but I’ve done it here merely to point out that sometimes you just luck out. In this case it truly was a matter of chance.

In my mind, the DePolo Orchestral Suite makes the video. Hope you enjoy the show.

To learn more about these composers and their music, follow this link. 

 

U.S. Navy Diving and Aviation Safety

Blood pressure is not the only silent medical killer. Hypoxia is also, and unlike chronically elevated blood pressure, it cripples within minutes, or seconds.

Hypoxia, a condition defined by lower than normal inspired oxygen levels, has killed divers during rebreather malfunctions, and it has killed pilots and passengers, as in the 1999 case of loss of cabin pressure in a Lear Jet that killed professional golfer Payne Stewart and his entourage and aircrew. Based on Air Traffic Control transcripts, that fatal decompression occurred somewhere between an altitude of 23,000 feet and 36,500 ft.

In most aircraft hypoxia incidents, onset is rapid, and no publically releasable record is left behind. The following recording is an exception, an audio recording of an hypoxia emergency during a Kalitta Air cargo flight.

Due to the seriousness of hypoxia in flight, military aircrew have to take recurrent hypoxia recognition training, often in a hypobaric (low pressure) chamber.

As the following video shows, hypoxia has the potential for quickly disabling you in the case of an airliner cabin depressurization.

Aircrew who must repeatedly take hypoxia recognition training are aware that such training comes with some element of risk. Rapid exposure to high altitude can produce painful and potentially dangerous decompression sickness (DCS) due to the formation of bubbles within the body’s blood vessels.

In a seminal Navy Experimental Diving Unit (NEDU) report published in 1991, LCDR Bruce Slobodnik, LCDR Marie Wallick and LCDR Jim Chimiak, M.D. noted that the incidence of decompression sickness in altitude chamber runs from 1986 through 1989 was 0.16%, including both aviation physiology trainees and medical attendants at the Naval Aerospace Medical Institute. Navy-wide the DCS incidence “for all students participating in aviation physiology training for 1988 was 0.15%”. If you were one of the 1 and a half students out of a thousand being treated for painful decompression sickness, you would treasure a way to receive the same hypoxia recognition training without risk of DCS.

With that in mind, and being aware of some preliminary studies (1-3), NEDU researchers performed a double blind study on twelve naïve subjects. A double-blind experimental design, where neither subject nor investigator knows which gas mixture is being provided for the test, is important in medical research to minimize investigator and subject bias. Slobodnik was a designated Naval Aerospace Physiologist, Wallick was a Navy Research Psychologist, and Chimiak was a Research Medical Officer. (Chimiak is currently the Medical Director at Divers Alert Network.)

Three hypoxic gas mixtures were tested (6.2% O2, 7.0% and 7.85% O2) for a planned total of 36 exposures. (Only 35 were completed due to non-test related problems in one subject.) Not surprisingly, average subject performance in a muscle-eye coordination test (two-dimensional compensatory tracking test) declined at the lower oxygen concentrations. [At the time of the testing (1990), the tracking test was a candidate for the Unified Triservice Cognitive Performance Assessment Battery (UTC-PAB)].

As a result of this 1990-1991 testing (4), NEDU proved a way of repeatedly inducing hypoxia without a vacuum chamber, and without the risk of DCS.

The Navy Aerospace Medical Research Laboratory built on that foundational research to build a device that safely produces hypoxia recognition training for aircrew. That device, a Reduced Oxygen Breathing Device is shown in this Navy photo.

070216-N-6247M-009 Whidbey Island, Wash. (Feb 16, 2007) Ð Lt. Cmdr. James McAllister, from San Diego, Calif. sits in the simulator during a test flight using the new Reduced Oxygen Breathing Device (ROBD). The ROBD is a portable device that delivers a mixture of air, nitrogen and oxygen to aircrew, simulating any desired altitude. Combined with a flight simulator the ultimate effect replicates an altitude induced hypoxia event. McAllister is the Director of the Aviation Survival Training Center at Whidbey Island. U.S. Navy photo by Mass Communication Specialist 1st Class Bruce McVicar (RELEASED)
Whidbey Island, Wash. (Feb 16, 2007) Lt. Cmdr. James McAllister, from San Diego, Calif. sits in the simulator during a test flight using the Reduced Oxygen Breathing Device (ROBD). The ROBD is a portable device that delivers a mixture of air, nitrogen and oxygen to aircrew, simulating any desired altitude. Combined with a flight simulator the ultimate effect replicates an altitude induced hypoxia event. McAllister is the Director of the Aviation Survival Training Center at Whidbey Island. U.S. Navy photo by Mass Communication Specialist 1st Class Bruce McVicar.

Although NEDU is best known for its pioneering work in deep sea and combat diving, it continues to provide support for the Air Force, Army and Marines in both altitude studies of life-saving equipment, and aircrew life support systems. Remarkably, the deepest diving complex in the world, certified for human occupancy, also has one of the highest altitude capabilities. It was certified to an altitude of 150,000 feet, and gets tested on occasion to altitudes near 100,000 feet. At 100,000 feet, there is only 1% of the oxygen available at sea level. Exposure to that altitude without a pressure suit and helmet would lead to almost instantaneous unconsciousness.

OSF FL 900
A test run to over 90,000 feet simulated altitude.

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  1. Herron DM. Hypobaric training of flight personnel without compromising quality of life. AGARD Conference Proceedings No. 396, p. 47-1-47-7.
  2. Collins WE, Mertens HW. Age, alcohol, and simulated altitude: effects on performance and Breathalyzer scores. Aviat. Space Environ Med, 1988; 59:1026-33.
  3. Baumgardner FW, Ernsting J, Holden R, Storm WF. Responses to hypoxia imposed by two methods. Preprints of the 1980 Annual Scientific Meeting of the Aerospace Medical Association, Anaheim, CA, p: 123.
  4. Slobodnik B, Wallick MT, Chimiak, JM. Effectiveness of oxygen-nitrogen gas mixtures in inducing hypoxia at 1 ATA. Navy Experimental Diving Unit Technical Report 04-91, June 1981.

 

How Will You Try to Kill Me?

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Émile Jean-Horace Vernet-The Angel of Death

It’s been over three years since I posted a cautionary tale about oxygen sensors in rebreathers, and the calamities they can cause. Since then, the toll of divers lured to their death has been steadily mounting. In one week alone in April 2016, at almost the same geographical latitude in Northern Florida, there were two diving fatalities involving rebreathers. It is an alarming and continuing trend.

I know a highly experienced diver who starts each dive by looking at his diving equipment, his underwater life support system, and asking it that title question: How will you try to kill me today?

This deep cave diver, equally at home with open circuit scuba and electronic rebreathers, is not a bold cave diver. He is exceptionally cautious, because he is also the U.S. Navy’s diving accident investigator. He has promised me that his diving equipment will never end up in our accident equipment cage.

He and I have seen far too many of the diving follies where underwater life support systems fail their divers. But the crucible in which those fatal failures are often born are errors of commission or omission by the deceased.

Carelessness and an attitude of “it can’t happen to me” seem all too prevalent, even among the best trained divers. Divers are human, and humans make mistakes. Statistically, those accidents happen across all lines of experience: from novice divers, to experienced professional and governmental divers, and even military divers. They all make mistakes that can, and often do, prove fatal.

It is exceedingly rare that a life support system fails all by itself, since by design they are robust, and have either simple, fool-proof designs, or redundancy. In theory a single failure should not bring a diver to his end.

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The “head”, triplicate oxygen sensors, oxygen solenoid and wiring leading to the rebreather CPU. Image from jj-ccr.com.

 

Are oxygen sensors trying to kill you? That depends on how old they are? Are they in date? Ignoring the expiration date on chocolate chip cookies probably won’t kill you, but ignoring the expiration date on oxygen sensors may well prove fatal. Complex systems like rebreathers depend upon critical subsystems that cannot be neglected without placing the diver at risk.

Oxygen sensors are usually found in triplicate, but if one or more are going bad during a dive, the diver and the rebreather can receive false warnings of oxygen content in the gas being breathed.  We have seen a rebreather computer “black box” record two sensor failures, and it’s CPU logic deduced that the single working sensor was the one in error.

The controller’s programmed logic forced it to ignore the good sensor, and thus the controller continued to open the oxygen solenoid and add oxygen in an attempt to make the two dying sensors read an appropriately high O2. Eventually, the diver, ignoring or not understanding various alarms he was being given, went unconscious due to an oxygen-induced seizure. His oxygen level was too high, not too low.

Unlike fuel for a car or airplane, you can have too much oxygen.

Oxygen sensors do not fail high, but they do fail low, due to age. Rebreather manufacturers should add that fact into their decision logic tree before triggering inaccurate alarms. But ultimately, it’s the diver’s responsibility to examine his own oxygen sensor readings and figure out what is happening. The analytical capability of the human brain should far exceed the capability of the rebreather CPU, at least for the foreseeable future.

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JAKSA high pressure 6-volt solenoid used in a Megalodon rebreather. NEDU photo.

Oxygen addition solenoids hold back the flow of oxygen from a rebreather oxygen bottle until a voltage pulse from the rebreather controller signals it to open momentarily. The oxygen flow path is normally kept closed by a spring inside the solenoid, holding a plunger down against its seat.

But solenoids can fail on occasion, which means they will not provide life giving oxygen to the diver. The diver must then either manually add oxygen using an addition valve, or switch to bailout gas appropriate for the depth.

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Cut-away diagram of a 24-volt Jaksa 200 bar solenoid.

Through either accident or design, divers have been known to invert their solenoid spring and plunger, thereby keeping the gas flow open. In that case, oxygen could not be controlled except by manually turning on and off the valve to the oxygen tank. Of course, knowing when oxygen is too low or too high would depend upon readings from the oxygen sensors.

Suffice it to say that such action would be extremely reckless. And if the oxygen sensors were old, and thus reading lower than the true oxygen partial pressure, the diver would be setting himself up for a fatal oxygen seizure. It has happened.

Assuming a solenoid has not been tampered with, alarms should warn the diver that either the solenoid has failed, or that the partial pressure of oxygen is dropping below tolerance limits.

But as the following figures reveal, if the diver does not react quickly enough to add oxygen manually, or switch to bail out gas, they might not make it to the surface.

The three figures below are screen captures from U.S. Navy software written by this author, that models various types of underwater breathing apparatus, rebreathers and scuba. In the setup of the model, an electronically controlled, constant PO2 rebreather is selected. In the next screen various rebreather parameters are selected, and in this case we model a very small oxygen bottle, simulating an oxygen solenoid failure during a dive. On another screen, a 60 feet sea water for 60 minutes dive is planned, with the swimming diver’s average oxygen consumption rate set at 1.5 standard liters per minute.

Screen shot 3Screen shot 2

 

 

 

 

 

 

 

 

 

On the large screen shot below, we see a black line representing diver depth as a function of time (increasing from the dashed grey line marked 0, to 60 fsw), a gray band of diver mouth pressure, and an all-important blue line showing the partial pressure of inspired oxygen as it initially increases as the diver descends, then overshoots, and finally settles off at the predetermined control level of oxygen partial pressure (in this case 1.3 atmospheres). Broken lines on the very bottom of the graph show automated activation of diluent add valve, oxygen add solenoid, and over pressure relief valve. Long horizontal colored dashes show critical levels of oxygen partial pressure, normal oxygen level (cyan) and the limit of consciousness (red).

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Screen shot of UBASim results after an ill-fated 60 fsw dive.

The oxygen solenoid fails 53.7 minutes into the dive, no longer adding oxygen. Therefore the diver’s inhaled oxygen level begins to drop. Rather than follow the emergency procedures, or perhaps being oblivious to the emergency, this simulated diver begins an ascent. As ambient pressure drops during the ascent, the drop in oxygen pressure increases.

In this particular example, 62.5 minutes after the dive began, and at a depth of 13.5 feet, the diver loses consciousness. With the loss of consciousness, the diver’s survival depends on many variables; whether he’s wearing a full face mask, whether he sinks or continues to ascend, or is rescued immediately by an attentive boat crew or buddy diver. It’s a crap shoot.

So basically, the rebreather tried to kill the diver, but he would only die if he ignored repeated warnings and neglected emergency procedures.

What about your rebreather’s carbon dioxide scrubber canister? Do you know what the canister duration will be in cold water at high work rates? Do you really know, or are you and the manufacturer guessing? What about the effect of depth, or helium or trimix gas mixes? Where is the data upon which you are betting your life, and how was it acquired?

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Scrubber canister and sodalime. NEDU Photo

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NEDU photo.

 

 

 

 

 

 

 

 

 

 

 

Sadly, few rebreathers have dependable and well calibrated carbon dioxide sensors; which is unfortunate because a depleted or “broken through” scrubber canister can kill you just as dead as a lack of oxygen. The only difference is a matter of speed; carbon dioxide will knock you out relatively slowly, compared to a lack of oxygen.

But if you think coming up from a dive with a headache is normal, then maybe you should rethink that. It could be that your rebreather is trying to kill you.

Samael_(Angel_of_Death)_Personification
Samael_(Angel_of_Death)

 

 

 


Eating Crow – Safe Water Temperatures for Scuba Regulators

CrowScientists and engineers love to argue, and unlike the case with politicians, compromise is not an option. Technologists speak for nature, for the truth of a universe which does not speak for itself. But when a technologist is wrong, they usually have to eat some crow, so to speak.

Stephen Hawkings, the famous cosmologist, freely admits his brilliant doctoral dissertation was wrong. Crow was eaten, and Hawkings moved on to a better, arguably more correct view of the universe.

Now, on a much less grand scale, this is my time for eating crow.

There has been quiet disagreement over the water temperature above which a scuba regulator is safe from free-flowing or icing up. Those untoward icing events either give the diver too much gas, or not enough. Neither event is good.

Based upon an apocryphal Canadian government study that I can’t seem to put my hands on anymore (government studies are rarely openly available), it has long been believed by the Canadians and Americans that in water temperatures of 38°F or above, regulator icing problems are unlikely. That temperature was selected because when testing older, low flow Canadian regulators, temperatures inside the regulator rarely dropped below 32°F when water temperature was 38°F.

Regulator ice
U.S. Navy photo.

As shown in an earlier blog post, in 42°F water and at high scuba bottle pressures (2500 psi) in instrumented second stage regulators (Sherwood Maximus) second stage internal temperature dropped below zero Celsius (32°F) during inspiration. During exhalation the temperature rose much higher, and the average measured temperature was above freezing. Nevertheless, that regulator free flowed at 40 minutes due to ice accumulation.

Presumably, a completely “safe” water temperature would have to be warmer than 42°F. But how much warmer?

My European colleagues have stated for a while that cold water regulator problems were possible at any temperature below 10°C, or 50°F. However, as far as I can tell that assertion was not based on experimental data. So as we began to search for the dividing line between safe and unsafe water temperatures in another brand of regulator, I assumed we’d find a safe temperature cooler than 50°F. For that analysis, we used a generic Brand X regulator.

To make a long story short, I was wrong.

To understand our analysis, you must first realize that scuba regulator freeze-up is a probabilistic event.  It cannot be predicted with certainty. Risk factors for an icing event are diving depth, scuba bottle pressure, ventilation (flow) rate, regulator design, and time. In engineering terms, mass and heat transfer flow rates, time and chance determine the outcome of a dive in cold water.

At NEDU, a regulator is tested at maximum anticipated depth and ventilated at a high flow rate (62.5 L/min) for a total period of 30 min. If the regulator free flows or stops flowing, an event is recorded and the time of the event is noted. Admittedly, the NEDU test is extremely rigorous, but it’s been used to select safe regulators for U.S. military use for years.

Tests were conducted at 38, 42, 45 and 50°F.

Next, an ordinal ranking of the performance for each regulator configuration and temperature combination was possible using an NEDU-defined probability-of-failure test statistic (Pf). This test statistic combines the number of tests of a specific configuration and temperature conducted and the elapsed time before freezing events occurred. Ordinal ranks were calculated using equation 1, Eqnwhere n is the number of dives conducted, E is a binary event defined as 0 if there is no freezing event and 1 if a freezing event occurs, t is the elapsed time to the freezing event from the start of the test (minutes), and k is an empirically determined constant equal to 0.3 and determined to provide reasonable probabilities, i is the index of summation.

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Click for a larger image.

Each data point in the graph to the left represents the average result from 5 regulators, with each test of 30-min or more duration. For conditions where no freezing events were observed at 30 min, additional dives were made for a 60-min duration.

As depicted, 40-regulator tests were completed, using 20 tests of the five primary second stages and 20 octopus or “secondary” second stages. Regression lines were computed for each data set. Interestingly, those lines proved to be parallel.

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A second stage of a typical scuba regulator. The bite block is in the diver’s mouth.

The “octopus” second stage regulator (the part going in a scuba diver’s mouth) differed from the primary only by the spring tension holding the regulator’s poppet valve shut. More negative mouth pressure is required to pull the valve open to get air than in the primary regulator.

The test statistic does not provide the probability that a given test article or regulator configuration will experience a freezing event at a given temperature. However, it does provide the ability to rank the freezing event performance of regulator configurations at various temperatures.

Our testing reveals that in spite of my predictions to the contrary, for the Brand X regulator our best estimate of a “safe” water temperature, defined as Pf = 0, is roughly 53°F for the standard or “primary” second stage regulator and 49° F for the octopus or secondary regulator.

For all practical purposes, the European convention of 50°F (10°C) is close enough.

Eating crow is not so bad. Some think it tastes a little like chicken.

Separator smallEquation 1 came from J.R. Clarke and M. Rainone, Evaluation of Sherwood Scuba Regulators for use in Cold Water, NEDU Technical Report 9-95, July 1995.

Diving a Rebreather in Frigid Water: Canister Concerns

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As evidenced by Under the Pole diving expeditions, rebreathers are being used in some of the most isolated and frigid places in the world. Some of those dive missions are surprisingly deep (111 meters, 330 feet) and long, about 2 hours.

That gives me cause for pause.

I suspect most divers are aware of the 1/3 rule for gas consumption on an open circuit (scuba) cave dive. You should use no more than 1/3 of your air supply on the way in, leaving you with 1/3 for the trip out, and 1/3 of your gas supply available in reserve. Sadly, even that amount of reserve has not saved all cave divers.

Now that cave divers are using rebreathers, the rules, at least for some, have changed. Some savvy rebreather cave divers use the rule of doubles: Always have twice as much oxygen, twice as much diluent, and twice as much canister as you think you’ll need. That plus an open-circuit or semi-closed circuit bailout should keep you safe — in theory.

Gas supply is easy to measure throughout a dive; there is a pressure gauge for all gases. But what about canister duration? Most divers assume they will have more canister duration available than gas supply; which means they don’t need to worry about canister duration. That would be a good thing, if it were true. After all, how many manufacturers provide expected canister durations for various work rates and water temperatures? Maybe, none? Or certainly very few.

I would be very surprised if manufacturers could say with certainty that during a two hour dive in -2°C (28°F) water, at depths to 111 meters that the scrubber can provide double the duration needed. That would be four hours in -2°C water, at all potential diver work rates.

Some of you may say, “Under-the-ice-diving is not like cave diving, so the doubles rule is too conservative.” I invite you to think again. Under polar ice, is there ready access to the surface? Not unless you’re diving directly under the through-ice bore hole the entire time.

In the U.S. Navy experience, obtaining useful data on canister durations from manufacturers is difficult. Duration data as a function of temperature is practically nonexistent. Therefore I will share the following information gleamed from scrubber canister testing in extreme environments by the Navy. While this blogger cannot reveal canister durations for military rebreathers, the information on the coefficient of varation (COV) is not protected. (There is no way to figure out what a canister duration is based solely on the COV.)

The following 4-minute video gives a good introduction to the coefficient of variation.

https://youtu.be/XXngxFm_d5c://

All rebreather divers should know that canister performance declines in an accelerating manner as water temperature drops between 50°F and 28°F. But what your rebreather manufacturer may not know is that the innate variability of canister durations also increases as water temperature drops. The Navy has found that trend in all types of rebreathers.

So, while canister durations drop considerably in cold water, you’re also less certain about what your canister’s endurance is going to be, because of the increase in duration variability. When canister duration drops and variability increases, a diver’s margin of safety becomes a gamble. Personally, I don’t like to gamble under water.

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Coefficient of variation (COV, mean duration divided by the standard deviation) of a typical rebreather. Each data point is the mean of five canisters (n=5).

In the U.S. Navy, published canister durations take into account mean canister performance, and variability. That is accomplished through the use of 95% prediction intervals. The greater the variability in canister duration, the lower the published duration.

This method of determining safe canister durations has been in use by the U.S. Navy since 1999. However, I do not know if manufacturers use similar statistically-based methods for publishing canister durations. If they or you do not take duration variability into account as you dive cold, you may be in for a shock. Due to the nature of statistics, you may have 9 deep, cold dives with no CO2 problems, but find yourself in bad shape on the 10th dive.

If you did have a CO2 problem, it wouldn’t necessarily be anyone’s fault: it could just be a result of canister variability in action.

So, diver beware. Give yourself plenty of leeway in planning rebreather dives in frigid waters. After all, you do not want to become a statistic, caused ironically by statistics.

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If you have an interest in understanding the derivation of the prediction interval equation and its application, two videos of lectures by Dr. Simcha Pollack from St. John’s University may be helpful. Part I is found here, and Part 2 is found here.

Thanks to Gene Hobbs and the Rubicon Foundation, NEDU’s original report on the use of prediction limits to establish published canister durations is found here.