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Decompression, Deep Stops and the Pursuit of Precision in a Complex World

In this first of a four-part series, Global Underwater Explorers’ (GUE) founder and president Jarrod Jablonski explores the historical development of GUE decompression protocols, with a focus on technical diving and the evolving trends in decompression research.

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by Jarrod Jablonski

Introduction:

This four-part series will explore the historical development of Global Underwater Explorers’ (GUE) decompression protocols with a focus on technical diving and the evolving trends in decompression research. The series will include aspects important in recreational diving but with a greater focus on the variables affecting technical divers. Those with less technical experience will hopefully benefit from a substantial number of reference materials linked throughout the series. These support materials and the balanced perspectives I am striving to present are designed to encourage a broader grasp of this complex subject. I also wish to take a few chances with this series by presenting some controversial positions in the hope they will stimulate open discussion and deeper consideration on all sides. 

In the interest of disclosure, I would like to foreground my belief that it is impossible to reach a definitive conclusion regarding the most efficient or the safest decompression procedures, though such determinations depend largely on how you define these terms. Indeed, it is a lack of certainty that motivates me to write this series since most of us will experience our entire diving careers with uncertain knowledge and while evaluating contradictory advice. It is my intent to provide a balanced overview while asserting that one should pursue a measured response to the dictates of pundits on all sides of the debate, myself included. Most importantly, I will explore the idea that many details may not be as significant as we typically imagine. For the sake of informed consideration, we will even explore the idea that both sides—in fact, all of us—are wrong and that we might know less about decompression sickness than it appears. 

One last word on the structure of this series. My intent here is more about establishing a broad perspective and less about arguing a narrow view of this elaborate subject. To this end, I hope you will join the discussion by posting in our comments, or that some of these ideas might stimulate discussions in your various communities. Let’s get started.

Part One: Contextualizing the problem of decompression.

Humans have been exploring the underwater world for hundreds of years, driven by a seemingly insatiable curiosity to reach ever farther below the mysterious surface. The brevity of early breath-hold dives gave way to technology with advances in diving bells in the 16th and 17th century and led to the development of independent diving with the Fleuss rebreather unit around 100 years later. The Fluess device was a self-contained underwater breathing apparatus (scuba) and helped develop the future of untethered diving, although excursions would remain short and/or shallow for many years to come. 

Developing technology that could support extended time while working underwater was a necessary part of the construction of bridges such as the Brooklyn Bridge during the 1870s. This was accomplished by constructing underwater rooms that were pressurized to keep them dry. Few people would think of these immersions as “diving,” but the extended time breathing gas at pressure highlighted a problem that would become known as decompression sickness, which was later included as one of two distinct pathophysiologies.

The Brooklyn Bridge under construction.
J.S. Haldane

The desire to understand and ultimately prevent the occurrence of decompression-related injury spans the life and interest of many researchers, nations, and individuals. In order to better appreciate some historical context, we can refer to the early work of Robert Boyle (1627 – 1691) who identified pressure-related problems when he spotted bubbles in the eye of a decompressed snake. Those not familiar with Robert Boyle may be familiar with  J.S. Haldane (1860 – 1936) who is credited with establishing the first set of decompression tables while under commission by the Royal Navy. 

Albert Buhlmann

Meanwhile, individuals like Albert Buhlmann (1923 – 1994) helped develop the science of decompression during a rich university career, including work for military, commercial, and even recreational diving interests. Decompression enthusiasts are likely familiar with early work done by researchers like Brian Hills (1934 – 2006) who focused on incorporating the formation of bubbles into decompression algorithms. Certainly, these few people do not properly represent the science of decompression, and we could list dozens of other important individuals who heavily shaped the science. My intent here is only to highlight the span of more than 5,000 years during which humans have been reaching ever farther below the watery surface. This history also includes roughly 200 years of research by a wide range of individuals, organizations, and governments seeking to understand the complications of breathing gas under increased pressure.  

The development of decompression practices proved successful even in their first use with caisson work, notably reducing the problems associated with breathing gas while under pressure. This progress extended into diving activity, and included the first tables produced by Haldane in 1908 for the British Admiralty. His tables remained in use by the Royal Navy until 1955. These developments supported longer and more aggressive diving activity, inaugurating a new age of discoveries and their associated challenges. 

Advancement tends to remove some or even many risks but also creates the possibility for new problems. These might develop from the ability to push boundaries farther or because more people can become involved in a given activity. We tend to build upon early success, refining safety protocols and treating a progressively smaller subset of incidents. Over time, the strategies to reduce injury become more refined and, to some extent, more individualized. 

For example, early cities were very dangerous places before fire protection, building standards, health codes, and similar protections. These practices became more refined, focusing on workers, home dwellers, children, and others. Most advanced societies are now quite safe, and additional levels of refinement continue to tease individual safety concerns while striving for the elimination of accidents—requiring notably more effort and expense to remove progressively smaller amounts of risk. It is hard to clearly identify our place on this curve when it comes to decompression sickness, but we appear fairly well into the diminishing returns part of the process. 

Exploring high-pressure environments began when elaborate mining, tunneling, and bridge-building projects resulted in problems of unknown origin. In subsequent years, we identified an arguably well-defined illness with a relatively clear causality. Many details remain vague, but our ability to characterize the problem supported the development of decompression strategies that significantly reduced injuries associated with breathing gas under pressure. These developments resulted in algorithms that predicted safe exposures and were codified into decompression tables and used for progressively deeper diving excursions. 

Today, decompression-related problems are extremely uncommon, especially within the recreational diving community. We now find ourselves mostly managing problems within a small subset of incidents. We strive for clarity among these low-probability injuries, seeking to improve or at least maintain safe guidelines while expanding our understanding. We typically acknowledge some influence from pre-existing conditions that, for whatever collection of reasons, might make a person more susceptible to injury.  We also strive to discourage diving activity that violates defined ascent speed or time limits while trying to establish a solid understanding of the constellation of problems we call decompression sickness. 

Meanwhile, the safety of decompression among those who use algorithms within uncharted territory remains less certain. Individuals who dive very deep and/or over very long times may be outside the range where safe dives can be predicted. For example, a decompression algorithm developed for dives up to 30m/100 ft for immersions as long as one hour may or may not extrapolate for dives of longer duration and depth. It requires a great many dives in order to verify that a particular exposure will result in low risk for most people. Given the high cost, added complexity, and safety risk, these important data points are particularly limited with dives that are very deep and/or long. This is something we return to in a later discussion. 

For the moment, we are mostly focused on dives with good supporting data and where notable improvement appears unlikely. Much of the sometimes raucous debate over decompression “correctness” involves teasing arguably minor benefits from already very low levels of risk. Can we change this reality? Can we find something that brings substantial improvement, perhaps allowing much longer dives with even shorter decompressions?

In thinking about the “problem” of decompression, we understand that scuba diving increases the pressure around us, also known as increased ambient pressure.  We are now breathing gas that is at a higher pressure than normally exists in our body. The molecules we are breathing become dissolved in our blood, where they are transferred during normal circulation and accumulate in the tissues of our body. This occurs until the tissues are “full” or, more precisely, until they are saturated at the new inspired gas pressure. Reductions in the surrounding pressure reverse the gradient and encourage the molecules to leave the tissues through the blood. 

Algorithms that strive to characterize this process are known as dissolved gas models. The transfer of dissolved gas from the tissues often results in the formation of bubbles in a way that is similar to releasing pressure from a carbonated beverage. Dissolved gas models do not ignore the risk of bubbles but also do not attempt to directly control their development. Attempts to directly limit the formation and development of bubbles are known as bubble models. 

We imagine that both dissolved gas and bubbles are relevant and also that other individual factors play some role. The problems in finding the best strategy are numerous, but most will be managed in a later discussion. For now, I wish to highlight that tracking of dissolved gas has been our primary strategy, consuming all but a relative handful of the many decompression experiments through the history of decompression research. 

Modeling bubbles is inevitably more theoretical and based upon mathematically derived predictions about bubble behavior, sometimes supported by lab experiments that measure the likelihood of bubble formation under certain conditions. Models can also be crafted as “dual-phase,” meaning they anticipate bubble development but also track dissolved gas, striving to ensure that both are within safe parameters. In all cases, we tend to develop more confidence in models that are tested empirically, though they may also be compared to a database of outcomes, supporting evaluation and calibration of the model particulars.  The most modern approach is trending toward probabilistic models, and we will explore these in future treatment.  

The presence of bubbles during decompression is well known, and to some extent is measurable by Doppler testing, which can detect bubbles in the venous part of the circulatory system. The venous system receives blood from tissues that are eliminating gas absorbed while diving, so the presence of at least some bubbles are expected. Unfortunately, there are many complications to the use of Doppler as a means to gauge decompression efficiency. Measures of venous bubbles may be useful for predicting decompression stress in populations of divers, but it fails to be a reliable measure of symptoms in an individual diver.  

Despite the complications, most researchers agree that bubbles (though not necessarily those detectable in the venous blood) are a critical part of the causal chain. The consensus seems to be that these bubbles either directly cause decompression sickness and/or contribute to its severity. Even if we assume bubbles cause all decompression-related symptoms, predicting their effects might be overly complicated. Albert Buhlmann, a great contributor to dissolved gas models, knew about and acknowledged the relevance of bubbles. He nonetheless focused upon refining dissolved gas strategies as a way to minimize risk of decompression sickness. We don’t yet know if this is the best strategy, but it has been quite successful at allowing a very low level of risk during most dives. 

Tracking other markers that might affect symptoms of decompression sickness is conceivable and is part of a body of research that seeks to better understand the full scope of decompression problems. For example, researchers are exploring immune-response factors, including genetic influences that might be involved in the body’s reaction to decompression. We might also learn more about heart rate variability (HRV), which has become popular as a way to measure physiological stress in the world of sport and exercise, and its potential involvement in DCS. These or other techniques could conceivably be used to establish upper limits on the stress accumulation that occurs during decompression, presumably avoiding some upper threshold before symptoms become problematic. 

We might also find ways to reduce decompression time by eliminating or changing the gas at the source of the problem. For example, we might eventually manage to use a liquid carrier for the oxygen that sustains our lives. By eliminating or greatly reducing use of gases like nitrogen or helium, we should be able to notably change the relevance of bubbling during changes in pressure. Or, we might develop ways to prevent or greatly reduce the risk of bubble formation by using drugs or other prophylactics that could physically alter the circumstances under which bubbles form. These ideas and many others have been explored and may hold promise, but nothing that greatly departs from current practice appears likely in the foreseeable future. 

Jarrod Jablonski with during deco. Photo by David Rhea.

Despite reasonable uncertainty about many details in decompression sickness, including the exact incident rate of DCS, which is unknown, divers following conventional decompression tables and diving within well-established limits have a very low risk of injury with rates of  0.01-0.1% per dive or about 1-10 incidents per 10,000 dives (the higher end reflecting rates for commercial dives, the lower end reflecting technical, scientific, and recreational dives). The risk is greater for certain types of very aggressive dives, but we will explore that aspect in a later discussion. Regardless of the actual risk, few divers would knowingly choose a less efficient ascent profile if a better option was available. 

The pursuit of decompression efficiency is particularly relevant for the group of divers known as technical divers. For these divers, arguably small differences can involve additional hours decompressing in the water. These divers have been particularly interested in the problem of bubbles that might develop during long ascents in deep water.  Many tech divers followed early research that concluded slower ascents from depth could greatly reduce decompression time. For some years, the convention of using “deep stops” to slow a diver’s ascent seemed to be the best way forward. Yet, new research argues they are actually part of the problem. Whether or not you feel sure about the value of deep stops, I hope you will join us for some engaging online discussions and especially for future sections as we dig deeper into areas that do not commonly appear in discussions orbiting decompression or deep stops. I look forward to reading your thoughts in the comments section and hope you will join part two of our series: “Tech Divers, Deep Stops, and the Coming Apocalypse”.

Please come back in two weeks when we release the next part in this series from President Jarrod Jablonski.


Jarrod is an avid explorer, researcher, author, and instructor who teaches and dives in oceans and caves around the world. Trained as a geologist, Jarrod is the founder and president of GUE and CEO of Halcyon and Extreme Exposure while remaining active in conservation, exploration, and filming projects worldwide. His explorations regularly place him in the most remote locations in the world, including numerous world record cave dives with total immersions near 30 hours. Jarrod is also an author with dozens of publications, including three books.

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One Way The World Learns to Mermaid: The Mer-spective from PADI’s Karl Shreeves

InDepth’s editor-in-chief Michael Menduno reached out to PADI veteran Karl Shreeves to explore the trending global phenomena of mermaiding….

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by Michael Menduno

Header image and photos courtesy of PADI Inc. unless noted.

InDepth’s editor-in-chief Michael Menduno reached out to PADI veteran Karl Shreeves to explore the trending global phenomena of mermaiding, which may well surpass tech diving in terms of sheer numbers in the not so distant future! While you shouldn’t expect to see a Global Underwater Explorers  (GUE) “MER 1” class anytime soon, it’s fair to say that mermaiding is here to stay—and that’s arguably a good thing. Here’s why!

As a uniquely dominant force in the $2-3 billion worldwide sport diving market, with nearly 6600 affiliated dive centers and resorts and over 128,000 members, it’s not surprising that privately-held PADI Inc., the self-proclaimed, “Way The World Learns To Dive,” is one of the most closely watched and talked about companies in the business. 

Over the last thirty years, since the emergence of technical diving, PADI has arguably relied on others—“Brand X” in PADI parlance— to bring technological innovation to the diving market while keeping a careful eye on their progress. Once a sufficient market develops, PADI moves in to adopt, standardize, promote, and profit from the innovation, and help popularize and fuel its growth by virtue of PADI’s sheer scale, often to the dismay of competitors. It’s a tried and true model that the organization has applied to nitrox, open-circuit tech diving, recreational rebreathers, and recently even freediving.

So, it was perhaps inevitable, given the tremendous growth and interest in mermaiding over the last decade, along with the entry into the market by Scuba Schools International (SSI) and NAUI, that PADI would pick up the tail, err trail, and offer its own mermaid program aimed at aquatic consumers, and its own teeming instructor ranks. Τhe fifty-five year old training behemoth launched the program in December 2020 and kicked it into high gear last April, with a TikTok-savvy, mono-a-mono, Guinness World Record extravaganza —the largest mermaid show on Earth—held at the Atlantis Sanya hotel aquarium, in Sanya China. Cirque du Soleil move over! 

Accordingly, to get a perspective on the market, we reached out to PADI’s original tekkie, technical development executive Karl Shreeves, who helped field its mermaid program, and was instrumental in the development of PADI’s nitrox and tech diving courses. Here’s what the veteran educator had to say. 

InDepth: To start, let me ask you: How did PADI get involved in mermaiding? When did you start looking at it and thinking about creating a training program?

Karl Shreeves: PADI had actually gotten involved with mermaiding several years ago. We had several instructors who had become part of the existing mermaiding community that wanted to offer a distinctive specialty. So, they submitted the distinctive specialties outlines, and we approved them. And then it started to grow, and the interest started to grow, and we began to get calls for us to create a program like we have for freediving and scuba diving and other types of diving. 

So, we started developing that in 2018 into early 2019. At the time, for us, and by us, I mean what was then the mainstream diving community apart from mermaiding, it was pretty small potatoes. Mermaiding already existed. It popped up on its own track separately from diving. There were already mermaiding schools and people doing it who did not come from a diving background at all. They just got into mermaiding. 

Did things slow down with the pandemic?

On the contrary. The interesting thing was that the pandemic seemed to propel it. And the reason? What do water enthusiasts do when they can’t travel? They get into the local pool. The pandemic helped freediving as well, and in some areas, local diving did well. Scuba divers quickly figured out that, “Well, I can’t see as far in my local lake as I can in Grand Cayman, but it’s actually pretty cool.” They get a trained eye and a perspective. 

But as the pandemic forced us to stay closer to home, there was a growing interest among the traditional diving community in this form of diving because, unlike freediving and scuba diving, all of a sudden, there was an expressive form of diving. It’s underwater dance. The costumes are beautiful. Obviously, it borrows from other kinds of diving. They all borrow from each other, right? 

But you know, especially if you were going to be primarily in a pool, it gave water enthusiasts a new craft that is well suited to the swimming pool. While there is open water mermaiding, as you know, a lot of it is purely in a swimming pool or the various dedicated super pools, and it’s a really good fit there. So mermaiding is a new angle, if you will, for expressing yourself.

It’s a performance art in many ways, like synchronized swimming or water ballet.

Right. Of course, there are a lot of people who come from the diving side and they say, “Well, it’s a form of freediving.” But really, it’s not.” It shares a lot from freediving. It has borrowed a lot from free diving, but it’s really different. 

Freediving tends to be more about the performance of depth and duration. It’s an athletic accomplishment. And again, there’s overlap. I’m speaking a bit in absolutes, but don’t misunderstand me. Mermaiding is more about individual expression and fantasy made real—an ability to touch people in a way that goes as far as wearing make-up as well as some elaborate costumes. And yet, having to be able to swim. And not just swim, but to look elegant and interact with people. 

That’s where it’s got an appeal because that hasn’t previously existed much in diving. Probably the closest thing would be being an underwater model. Ironically, because of the pandemic, and lock-downs, I wasn’t able to be one of the shooters for our Mermaid eLearning course. If there was ever a shoot I wanted to do it was that one!

Ha! You were deprived! What about the language? You use ‘mermaid’ to refer to both genders, not mermaids and mermen, or merfolk?

Funny you ask about “mermaid” as a term, because we actually explain it at the beginning of the course. “Mermaid” denotes gender in English, but in many languages the translated term means “human fish” and doesn’t indicate gender unless you add words to do so. Some in mermaiding use the terms “merfolk” and “merman” etc., but broadly, “mermaid” is the term everyone knows. So, the PADI materials use “mermaid” in the sense of “human fish” as in languages like Chinese, Japanese, Korean, and Vietnamese. But obviously, it’s not a female-only sport by a long shot. Lots of men are mermaid divers and PADI Mermaid Instructors.

I’m sure some of our readers see mermaiding as a trend, something new, but the concept and fascination with mermaids goes back a long way.

It’s not new. It goes back over 1,000 years. There is something about this idea of a human fish that has endured. If you look at the movie Splash, right? 1984. The sixth largest grossing movie in China was The Mermaid. And they are talking about a sequel now. The Korean drama I keep talking about, Legend of the Blue Sea, is one of the most successful dramas they’ve had. Very popular, and people still watch it aftermarket and buy it on DVD. So, this is not a flash in the pan. It’s actually a cross-cultural mythology that we’ve enjoyed as humans. If it were just one culture you’d say, eh… But it’s not. 

Every culture independently created this myth. Now the modern mermaid tends to be the European mermaid, and we talk about this in the course too. Why? Because it’s practical. The European mermaid’s bottom half is fish and top half is human. Very easy to create a swimmable costume. But some, you can do it with computer graphics, it’s a fish with a human face. But my point is that when we look at this as the dive community and say, “Oh, that’s just a bunch of people playing around.” Yeah, it is, but that’s not new. This has been around. So this is going to stay. Now that we have the ability for people to go play mermaid in a serious, fun way, they are going to keep doing it because it’s cool.

In some ways, it enables us to reach back through time and connect with this myth that’s embedded deep in the human psyche.

Once humanity starts to picture something, we find ways of making it happen. And that’s what’s happened to the thousand-year-old dream of being a human who can live in water. We found a way to make it real.

Talk to me a little about the size of the market. Obviously if PADI is getting into it, you must think there is sizable potential. I was surprised when I attended the ADEX show in Singapore in 2019, and they had a huge mermaid section. In fact, it was bigger than the tech diving section! They had 30 or 40 famous mermaids there. I didn’t know who they were, but the people knew them and cheered for them. It was amazing.

Well, as I said, parts of the dive community had adopted mermaiding. It was already growing globally. In fact, it’s really big in Asia in terms of its visibility, but there’s actually a pretty strong community around the world. There are communities in Europe. Here in California, they have a small mermaid convention that’s been held for several years in the Bay Area. It’s not huge but it’s there, and quite separate from diving. It’s about mermaids and mermaiding. They get in the water; they talk about mermaid stories and myths. They role play, and there’s also a little bit of cosplay. Ι think that is part of the fun for some people.

But to give you an idea of scale, when we finally launched the full version of the program within, I want to say, it was a month or two months, we had 500 instructors.

Photo courtesy of Julie Ferrara.
Wow. That’s surprising! Evidently there’s a lot of pent up demand.

Right? When you pick up that many instructors that fast, it’s two things. One, it is popular. Two, it’s already widespread because you don’t learn to mermaid and then reach instructor qualification in two months. You actually have to already have the qualifications. And what we’re seeing is two prongs of appeal. 

First, it’s opened the eyes of divers who’ve never looked at it before and are most certainly going, “That’s cool.” A lot of them are free divers, but some of them are scuba divers. They’re like, “I want to give that a go.” But then we are also seeing that it’s pulling from the original market—people just interested in mermaids who want to live out the fantasy, as it were. That gives it a lot of youth appeal, especially among younger children. 

What we’re finding is that attraction is growing because some of these people realize that it also brings them a connection to diving. It’s like, “I’m not only going to become a mermaid, but, if I want, I can grow towards becoming a diver as well.” Some people find that out in the course. Because, as you might expect, a lot of the mermaid instructors also have their fins in the freediving camp. Those people tend to do a really good job of instructing because they know the difference. They know the difference between mermaiding and freediving. So, they don’t try to make mermaid divers freedivers, but they do train the mermaids in the techniques that apply from one to the other. 

In fact, somebody was asking me about this. “Oh, it’s just a form of freediving.” And I said, “No, not really.” However, when you are a buddy, that is the safety diver in mermaiding, that’s when you’re closest to being a freediver because basically you have the same job.



Makes sense. Freediving has developed safety techniques and protocols, which I would imagine apply to mermaiding too, so that mermaids don’t blackout underwater?

Yeah, in fact mermaiding basically borrowed that most directly. So, while mermaids don’t do static apnea, they swim dynamically as free divers call it. In other words, there’s lots of horizontal movement, but depth isn’t too great. Of course, the more experienced ones still get down there pretty well. But as soon as you shift—”Okay, it’s my turn to be the buddy.”—the mermaid tail comes off, the mask goes on (which is optional if you’re the mermaid), and you wear bi-fins because you need to be able to help and maneuver quickly in the event of a problem. So, that’s probably where you have the most and the strongest connection to conventional freediving.

Mermaids wear monofins but they use bi-fins when being a safety?

Right. They are required to use bi-fins for safety because they need to be fast and maneuverable as a safety. But by definition, if you’re a mermaid, what kind of fin are you going to have? I suppose somebody might come up with a bi-fin mermaid look, but basically, it’s all monofin. They’re going to learn both to be successful in the course.

In freediving, they have the one up, one down system, or one up, one prepping, one down in a team of three, in order to rescue the diver in case of hypoxia. So, mermaids also have somebody watching them who is ready to intervene when they’re holding their breath underwater?

Exactly! Freediving has done a lot for all breath-hold diving, just like tech contributed to all scuba diving. Tech taught us to be tighter with teams and also offered a mindset and approach that has been picked up. The alternate air source originally came from tech. Likewise, freediving has influenced breath-hold diving, even basic snorkeling. Divers are taught that they have to take the snorkel out of their mouth when you’re doing a breath-hold dive, so you don’t breathe a lung full of water in the event of unconsciousness.

Mermaid under Ice. Video courtesy of Teppo Lallukka
Nope! That applies to snorkelers as well! 

Of course, if you’re old school like me, and you came up the other way, as soon as you start freediving you’ve got a habit that you’ve got to change. The habit you learned first is the one that sticks. In instructional psychology we are still trying to figure out why this is. Of course, new divers are getting the right habits from the beginning, so they’re not going to have to relearn them.

Yeah, I had that problem too. My freediving instructor had to keep reminding me to spit out my snorkel when I dived! You mentioned open water mermaiding. I’m familiar with mermaid performances but do they also go out and conduct mermaid dives? Would a mermaid say, “Hey, let’s put on our tails and go dive the kelp forest?”

Because there is so much crossover between the communities, you have people who enjoy mermaid diving, and this is what we covered in the advanced mermaid course. They go out and they mermaid in the open water. There can be many motivations.

There are certainly venues, you know the classic going back decades is Weeki Wachee, of course, where you can watch. And that is more serious mermaiding. Just put brackets around it. It’s a little different from what a recreational mermaid learns. But it’s still the idea. 

Mermaids like to be in a natural environment and watch each other. If you are somewhere warm and nice—like Grand Cayman or Bonaire—and you are surrounded by beauty, it’s fun to go mermaiding. And if you’ve got underwater photographers who might want to take pictures of you, all the better. 

Are you aware of the Korean drama, “Legend of the Blue Sea?” It’s set in Korea but it begins somewhere in the mid-Pacific. The actress who plays the mermaid is swimming around coral and gorgeous stuff. The story is about how she swims all the way to Korea. So that was the performance. In recreational mermaiding, they have fun doing this. It’s something that can be done together in nature. In that case, they typically wear masks so they can see clearly, and they’ll swim down and see the fish. So, it’s a neat little aspect of mermaiding.

That’s right, you need a dive mask, not swim goggles, because you wouldn’t be able to equalize.

Right, and that’s another area where mermaiding differs from other forms of diving. The mask is optional. Some people prefer them, and or wear contact lenses that need to be kept dry. Conversely, in a place that’s not going to bother the eyes, where you see well enough to navigate, some will forgo the mask altogether. In the China video, you saw both.

Let’s talk a little about what has been in place prior to PADI’s and other training agencies’ entrance into mermaiding. How did people learn to be mermaids? I do know there are several schools out there like the LA Mermaid School, and I think Weeki Wachee has a program as well. That’s likely some of it.
Photo courtesy of Julie Ferrara.

Well, it’s kind of all over the map, like what you see in most swimming programs or water programs. There are numerous mermaid schools, as you call them, and there would be a ranking of typically a beginner and then an intermediate level and so on. I would say that—and I want to be sure I’m talking generally here because there are exceptions all over, things are starting to solidify, and community standards are evolving. However, generally compared to what diving offers many mermaid programs were comparatively unsophisticated but safe as far as I could tell. I saw nothing that looked unsafe. Some of them were pool-only and you always have grown-ups there, because there are children in the program, things like that. On the other hand there are some very sophisticated professional mermaid schools like LA Mermaid School and the Weeki Wachee program that offer top notch professional training.

I think what diving has brought to mermaiding is our experience in water safety and integrating it with breath-hold diving. If you take a PADI program, for example, and you are going to be a mermaid diver, you don’t need to be anything else. You just need to be okay on the medical (as any diver of any type), have basic swimming ability, and we’ll take it from there. You don’t have to be a “diver.” You’ll learn what you need to know to be a mermaid, which includes the stuff that’s come over from the other forms of diving.

I looked at the requirements. You need to be able to swim of course.

Yeah. And if you get right down to it, almost all water sports have that. If you fall in the water, it would be good if you knew how to swim. Seems like a good basic safety concept.

Ha! I also thought it interesting that your mermaid programs were open to pre-teens.

Yeah, it’s breath-hold diving, we don’t have the concerns we have with scuba. There’s not a risk of lung overexpansion injuries. We’re not concerned with the kind of depths that limit the junior divers to about 21 m/70 ft. On top of that, this is where we are able to borrow from the community that was there before we got involved. Traditional mermaid courses brought in kids. Kids do this great. They love it. They’ve already been doing it. So it’s not like we had to craft something new to make it fun for kids. Kids already know it’s fun.

Photo courtesy of Julie Ferrara, PADI Mermaid Instructor Trainer and owner of Freedive Cozumel 
We talk a lot in our industry about getting more young people into diving, given the increasing average age of the scuba diving community. Looks to me like mermaiding has the potential to get more young people underwater which is what we want, right?

Absolutely, but also what you’re describing is Western-centric, and changing. We are seeing more young people getting certified. But when you go to the Eastern Hemisphere, it’s like our generation was when we were in our 20s and 30s. That’s who is going diving, the young people. And it’s huge, and I would say it’s much more social there as well. 

The ADEX shows are filled with young people. It’s a very different demographic than the US or Europe.

There is a senior crowd there as well. Interestingly, for a long time PADI Japan was top age heavy because of the demographic of their country, but now that is changing as more young people get involved.

Traditionally, Asian cultures have been better at revering the older generation than Western cultures, because they recognize that’s where wisdom lies. So, you bring the innovation and the enthusiasm of youth, and you pair it with the wisdom and lessons of the past. That’s where you get a really strong community. You can probably tell: I really admire that they bring that to our diving community.

PADI has a bazillion dive centres around the world. Are we going to start seeing mermaid programs and communities popping up everywhere?

I would say yes. It’s happening as we speak. I mean it has never happened before: a program was a fringe program, a specialty, that was going to be it. The market was that small. But like I said, the pandemic changed that like it changed so many things. We’ve never seen a program that went from essentially a fringe activity to something worthy of our full support with e-learning in a year and a half! I’ll tell you what, I’ve never had to type so fast in my life.

To me it’s exciting. It’s like, wow. Because diving could either have fallen on its face during what happened or it could do something new. And we’ve done something new. I mean it wasn’t “new new,” but it was new in the expansion and the attention it got and that caused it to grow. The community is even plugging into dedicated deep pools like K-26 in Korea, one of those purpose-built deep pools that goes down to 26 m/85 ft.

Ah yes, deep pools. We have a story about deep pools in this issue.

There are a number in Europe, and there are some being planned for the US. Mermaiding blends beautifully with these. Because it’s more than a pool but not quite open water, but you’ve got the controlled conditions, and you have depth. The freediving community has taken advantage of these, too. Most of these facilities have underwater windows as well. So now, in addition to performance art, you have the potential to make it a spectator sport, if you will, in diving.

Yeah, that’s really interesting. Talk to me about training. We will, of course, include links with the article about your courses etc., but tell me, what do you need to learn to be a mermaid? What is the main focus of the courses?

As I mentioned, a lot of it is stuff you’d learn as a freediver, but applied to mermaids. The first thing you learn is about the costumes because that’s a little different. What is or is not an appropriate mermaid tail? Because you can buy some out there that are purely costumes, they are not for swimming. You learn to swim in them, so there is a huge emphasis on dolphin kick. You learn breathing techniques. But again, as a mermaid, you may not have a snorkel or whatever so you learn how to float, you learn how to wade as a mermaid. At the same time, you are also learning to be a safety buddy. What do I have to watch? I’ve got to have these fins on, things like that.

Is mermaiding a team activity built around two or three people mermaiding together? 

Like other forms of diving, you can’t paint too tight a box around that. But what we teach is that you have somebody watching you. It wouldn’t be considered reasonable to have two mermaids on the bottom and one safety diver. But if you were diving in threes, say, one person would go down and then come back up and then another goes down and comes up, and then the third, so it’s a bit like free diving. In open water, the safety diver might escort you through the last 5 m/15 ft. But in pool-based mermaiding, just like in pool-based free diving, the safety diver just stays on the surface. 

They learn skills that were developed in freediving but have been mermaid adapted. Like doing a duck dive, which is a little bit different in a tail than in bi-fins. You learn some skills unique to mermaiding. There are more flourishes. Like C-shaped turns and back turns and the mermaid kiss. All these things that they love to do. Team handshakes. They get into the performance a little bit. 

The instructor also has the latitude to help the mermaids try the makeup. And again, it’s not your typical Mary Kay. It has to be two things. It has to be waterproof and then if you’re in open water, it has to be environmentally friendly. It can’t be something that would hurt the environment. In our program, the mermaids are taught about the environment and our role as stewards, and they are encouraged to join the community of torchbearers who are trying to speak for the oceans. 

You incorporate ocean and water conservation!

Yeah. All our programs have that tie. If you love the ocean, you can see what’s happening. You can also see that we can do something about it. And the most important thing right now is we all have a voice and a purpose when we come together on that. 

I’ll run slightly into the weeds here, but you may have heard a few years ago that Drew [PADI CEO Drew Richardson] committed the PADI family to one billion torchbearers by 2050. And that’s actually not that huge a number. Drew also didn’t just pull that number out of the air. When you look at social tipping points, the amount of the population that has to adopt a new view before society tips in that direction, one billion is about half that number. 

That’s a laudable goal!

So, obviously, when we start talking to mermaids, a lot of those folks are a crowd from outside our normal sphere. Of course, we want them to understand about the oceans and have a connection to it.

Photo courtesy of Julie Ferrara, PADI Mermaid Instructor Trainer and owner of Freedive Cozumel 
They are ambassadors. They are performing for people who may not be water people.

The potential for a mermaid to get in front of non-divers is in some ways better and at least different. And so they are reaching a new audience. Look at Mermaid Linden . How many kids does she talk to? You start talking with her about the ocean, and you won’t leave without knowing that it’s in trouble, it’s worth saving, and we can do it. She’s reminding six-year olds that they can help.

That’s powerful. I don’t know that the scuba community even talks to six-year olds. Get them while they are young, right? Karl, you and your colleagues have been involved in the development of many, many training programs. Was there anything unique or challenging about creating a mermaid program?

I’d say, fortunately, we’ve done this enough that we have learned where to look. In the past, I would’ve said that the challenge might have been finding the experts that we needed to go over what you’ve done and help us look for gaps and things like that. I would say, if there was any challenge, it would be this, and that was when we got to the e-learning part. 

Because of the lockdowns and everything we were very limited in what we could do in terms of finding talent and locations and photographers. We always try our best to show as much multicultural diversity as possible in our products, but this one had to be shot entirely by our China team. We were able to get some stock photos and so on to show more than Asian faces, but you can tell, if you look at the program, that they handled the imaging for us. 

Photo courtesy of Julie Ferrara,

But I’ll have to say, if we had to have a challenge, I’ll take that one any day of the week. They did a great job with what they did. They found some really, really talented mermaids to act in the stills and videos. We found enough stock shots of other faces that we could show our diversity. Plus, anybody who knows us, knows that we are probably the most culturally diverse group in diving.

PADI is not the only agency to see an opportunity. SSI launched their mermaid program in 2018. NAUI launched theirs in 2020. As far as Global Underwater Explorers (GUE) is concerned, I don’t expect to see “MER 1” anytime soon. But who knows? Do you anticipate more agencies jumping in on the tail wagon, as it were?

Yes, I believe we are going to see others pick this up as well as it grows. Success breeds competition. It’s happening, but that’s cool. 

I remember once asking undersea pioneer Phil Nuytten, who invented the modern one-atmosphere suit, if he expected to have any competitors. He told me, “I hope we have competition. In fact, I hope we have a lot of competitors. Because if we don’t, it means that it wasn’t a very good idea.” I’m guessing that the people at SSI and NAUI are at least feeling validated!

Competition also keeps everyone sharp! 

All the better for the mermaids, right? You launched your program in December 2020, and then last April PADI held this huge extravaganza in China. It was what, the largest underwater mermaid show ever?

The event was held at Atlantis Sanya in China and it set a Guinness World Record in their giant aquarium. It involved more than 100 PADI Mermaid divers, plus support divers and topside personnel. The divers spent three days rehearsing a synchronized dive—you can imagine what it takes to get 100+ divers to descend at the same time and then swim in a coordinated manner. It was spectacular though—and had a lot of international coverage.

Are you ready to get your mer on? Push play!
I heard that the event got 170 million views on TikTok—OMG!—and PADI now has something like 600 mermaid instructors and 50 dive centers in China offering your mermaid program.

I don’t know the numbers off the top of my head, but yes, the PADI Mermaid Program has gotten a lot of attention around the world. More than 600 instructors in China alone sounds right – it’s been eye-opening.

Talk to me a little about technology. Do your courses deal with working with surface supplied gas, or scuba, or the use of nitrox as a pre-breathe? Would that be technical mermaiding? Ha!

It’s not within our program nor any of the programs you’ve mentioned, to my knowledge. It wouldn’t surprise me if we get there. Now I do know that the Weeki Wachee program, which has been around for years, is training professionals. There you have to be a scuba diver because you are going to breathe compressed air, if I am not mistaken. Of course, you have to know how important it is to be exhaling as you ascend. Exactly the opposite of what you would normally do as a free diver or mermaid diver. Right now, that kind of thing is outside of what recreational mermaiding, for lack of a better term, is about. But come ask me again in a few years. I’m serious. We saw freediving do it, right? You just said it—technical free diving. Whoever thought, oh, I can breathe up using a gas with a high oxygen fraction and stay down longer on my one breath. That’s helpful. Who knows? One of the cool things about diving is that divers tend to get what they want instead of what someone thinks they ought to want.

I was speaking to Virginia Hankins at the LA Mermaid School and SHEROES Entertainment that provide professional mermaids for film and photoshoots and professional engagements. They are trained to use underwater breathing equipment. She’s one of your instructor trainers.

Yes, absolutely. We were talking about “Legend of the Blue Sea” earlier, and I’m sure it was true in “Splash”—when you start talking about Hollywood productions, they are going to use scuba. Again, that’s beyond what we are teaching in our recreational program. It requires additional education.

Let’s talk about equipment. I attended Eric Albinsson’s webinar on PADI mermaiding. He said that the global mermaid tail market was valued at $80 million in 2020—that’s annual revenue, and was expected to grow to $150 million by 2026, a compound average growth rate (CAGR) of 9.5%. That blew me away!

I don’t know what number he’s quoting, but it’s definitely there. And again, it’s not new, if you think about it. In our courses, the minimum is a monofin. But look at the variety of tales in that China mermaid video. 

They’re exotic and amazing. Some of them look like a real biological tail!

Yeah, so there’s absolutely a market that’s growing. And it’s been there, but it’s accelerating. And again, the pandemic probably helped it.

Obviously, PADI sees this as a business opportunity, not just for itself, but for its dive centers, instructors, and professionals.

Absolutely. For one thing, it’s reaching a new market, and some of these people will likely get exposed to freediving and scuba. So, you get this neat cross-pollination of the three markets, or rather the three communities. The second thing is, it’s a great resource to use. If you have a pool, or if you go to a pool a lot, you can do a lot there. People can go all the way through mermaid without going to open water. So, the center can offer two full certifications, plus the experience. If I ran a dive center, I would definitely at least be dabbling in it right now. I don’t think I’d want to ignore it.

It seems to me it’s a lot like adding freediving to a scuba center.

It’s similar. Your upfront investment isn’t that high. If you’ve got an instructor who wants to get into it, that person trains up and they learn to teach. You don’t need to buy another compressor or a mixed gas blending system. If you’re already catering to freedivers, you’ve already got all that covered. So basically, you’re talking about adding mermaid tails.

Tails! There we go again. I’ve often thought our job as an industry is just to get people into the water. Create water enthusiasts and then they’ll find whatever pathways work for them. Mermaiding is another fun thing to do in the water. 
Last question: Where do you see this going? Where will mermaiding be ten or fifteen years from now?

Boy, that’s such a hard one to call because if you had asked me that question a year and a half ago, I would’ve said, “Well, maybe we’ll have a supplemental program someday.” And here we have a full e-Learning program we’re about to debut.

I don’t want to call this one. It’s going to grow. I can say that with confidence because it’s got the inertia now, it’s already happening, it’s already popular, and it’s global. There’s attention to it. It’s beautiful, it gets people in the water. There isn’t a whole lot to say against it. So, it’s going to be bigger. How much bigger? I don’t know. It could really take off in some communities that have not been connected to diving, where that visual appeal is important, and there are a lot of young people involved.  

Thanks Karl. Call me crazy, but I find all of this really interesting.

Additional Resources:

The Darker Side of Mermaids

Wired: Fantastically Wrong: The Murderous, Sometimes Sexy History of the Mermaid

The Filthy Mermaid: Got-To-Have-Goods for For Mermaids Gone Bad

Events:

MerFest International 2021 (South Haven, MI 20-22 August, 2021)

Mermaids In Paradise (Ramrod Key, Fl 15-22 September, 2021) 

Training:

Photo by Lila Jones

NAUI: Fantasy Becoming Reality – When Divers Become Mermaids

PADI: How To Become a Mermaid

Photo by Casey McNutt

SSI: Join An SSI Mermaid Program


Michael Menduno/M2 is InDepth’s editor-in-chief and an award-winning journalist and technologist who has written about diving and diving technology for more than 30 years. He coined the term “technical diving.” His magazine “aquaCORPS: The Journal for Technical Diving” (1990-1996), helped usher tech diving into mainstream sports diving and he produced the first tek.Conferences and Rebreather Forums 1.0 & 2.0. In addition to InDepth, Menduno serves as an editor/reporter for DAN Europe’s Alert Diver magazine, a contributing editor for X-Ray mag, and writes for DeeperBlue.com. He is on the board of the Historical Diving Society (USA), and a member of the Rebreather Training Council.

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Diving tables prescribe time limits at various depths. Within a given time limit (known as a no-decompression limit or NDL) a diver can make a slow but direct ascent to the surface. When divers stay longer than the NDL they must engage in delayed ascents, usually stopping every 3m/10feet for the time prescribed on their table. Apps allow for calculation of various profiles in electronic format and these programs are also used in decompression computers to calculate limits, ascent rates, and stop time in real-time during the dive.

An algorithm is a process or set of rules to be followed in calculations or other problem-solving operations, especially by a computer: "a basic algorithm for division".

Decompression in the context of diving derives from the reduction in ambient pressure experienced by the diver during the ascent at the end of a dive or hyperbaric exposure and refers to both the reduction in pressure and the process of allowing dissolved inert gases to be eliminated from the tissues during this reduction in pressure. When a diver descends in the water column the ambient pressure rises. Breathing gas is supplied at the same pressure as the surrounding water, and some of this gas dissolves into the diver's blood and other fluids. Inert gas continues to be taken up until the gas dissolved in the diver is in a state of equilibrium with the breathing gas in the diver's lungs, (see: "Saturation diving"), or the diver moves up in the water column and reduces the ambient pressure of the breathing gas until the inert gases dissolved in the tissues are at a higher concentration than the equilibrium state, and start diffusing out again. Dissolved inert gases such as nitrogen or helium can form bubbles in the blood and tissues of the diver if the partial pressures of the dissolved gases in the diver get too high above the ambient pressure. These bubbles and products of injury caused by the bubbles can cause damage to tissues known as decompression sickness, or "the bends". The immediate goal of controlled decompression is to avoid the development of symptoms of bubble formation in the tissues of the diver, and the long-term goal is to also avoid complications due to sub-clinical decompression injury.

 

Source: https://en.wikipedia.org/wiki/Decompression_practice

1909: 

FJ Keays described 3,692 cases of decompression sickness. He established recompression as the treatment of choice. He showed that there was a persistence of symptoms in 14% of Caisson workers who were not recompressed compared with 0.5% in who were. However, he admitted that recompression often failed in “serious” cases. These data were published again in 1912.

Decompression Illness (DCI) encompasses:
-Decompression Sickness (DCS)
-Arterial Gas Embolism (AGE)
Decompression Sickness (DCS): Time spent diving causes an excess of inert gas, such as nitrogen, to dissolve in the body. When a diver surfaces this dissolved gas may form bubbles, which then cause local damage to body tissues or obstruct small blood vessels. This can result in a wide range of symptoms including pain, weakness, dizziness or tingling.

Arterial Gas Embolism (AGE): Most commonly occurs when diving as a result of lung over-expansion injury, also known as pulmonary barotrauma. Air passes directly from the lungs into the arteries, blocking them. This causes a variety of sudden onset, stroke-like symptoms depending on the site of the blockage, such as one-sided weakness or loss of consciousness.

The technology for these underwater rooms began in 1792 when Robert Weldon developed a Caisson Lock for movement of boat traffic. The term caisson is French as borrowed from Italian cassone and means "large box". The concept was extended by Jacques Triger who invented the air lock, allowing a worker to transfer from low-pressure to high-pressure environments. In1841 Triger documented the first cases of decompression sickness in humans when two miners involved in pressurized caisson work developed symptoms.