By Jarrod Jablonski
Header photo courtesy of the GUE archives
The human quest to explore below the water’s surface began some 5,000 years ago . Since that time, our species has pursued deeper and longer immersions, charting a course through hundreds of years of diving activity and associated research. Many of the advances in procedure, technique, and equipment are a direct result of the compelling and valuable data and experience documented during underwater explorations. As with many novel activities, this process of advancement required pushing physical and intellectual barriers.
During the 1980s and 90s, advances in technology supported an activity that became known as technical diving. This diving led to the development of ascent practices which were somewhat different from those of scientific, military, and commercial divers. A unique set of needs and limited relevant examples encouraged a great deal of experimentation among these early explorers, including adjustments to breathing gases and the distribution of decompression stops used during their ascent. Some technical divers began using a slower ascent from depth, in the hope this would control the formation of bubbles. These slow ascents became known as “deep stops” and were practiced in the hope they could reduce decompression stress and/or shorten decompression time.
In fact, the idea of bubble control was not new. During the 1960s, physiologist Brian Hills sought to characterize the profiles of pearl divers who had been operating since the late 1800s. These divers were interesting because they were ascending in two-thirds of the time required by Navy tables, a time that would cut even more decompression from most modern-day ascent schedules. Hills believed the reduced decompression times were the result of a unique ascent profile, including stops deeper than those called for by the Navy tables. Years later, technical diving explorers started adopting similar techniques while reporting reductions in total decompression time. It is difficult to qualify if this perceived success was actually occurring since the groups were relatively small, not carefully monitored, and simultaneously adjusting numerous other factors during their ascent. Even absent these complications, the generally low risk of decompression sickness can greatly complicate evaluations between different strategies.
The enthusiasm for deep stops likely reached its peak in the late 1990s and was dealt a serious blow by the previously discussed Navy Experimental Diving Unit (NEDU) study that was released in 2011. This study, and others, propose that deep stops are less efficient and may actually increase the risk of decompression sickness. The reader should refer to part three of this series for discussion and references. This series contends that opposition to deep stops is supported by prevailing research, but that a range of other variables need to be considered in order to effectively develop best practices. These aspects are particularly relevant to experienced divers, who report decompression sickness problems when eliminating slower ascents from depth.
It is not my intent to re-litigate the previous three sections of this article, but an interesting, and I believe, underappreciated aspect of Brian Hills’ pearl diver study provides a nice segue. What I find most interesting are the roughly 3,000 deaths and injuries of an unknown quantity that helped shape those unique ascent profiles. In other words, how was this conclusion affected by the elimination of those who are more susceptible to injury, and how much was due to a lack of rigor in the study ? Hills concluded that the success of the profiles was “due to the much deeper initial decompression stops used” by the pearl divers. In a similar way, technical divers took note of the history, the encouragement from experts, and the perceived success by those in their community.
Given new and mounting evidence against deep stops, can we now definitively conclude that Hills, the pearl divers, and the tech divers were wrong? Are we sure the perceived success was imagined? If some success occurred, was it more about the generally low levels of risk in decompression sickness? Or could something else worth considering be at play? Asked another way, we might inquire how the conclusions reached by Hills and those technical divers are different from the way modern-day decompression tables have come into being.
The history of pearl diving and deep stops is very different from that of most decompression research in at least two substantial ways. The first difference has to do with methodologies, and the second with objectives. In terms of methodology, most decompression research is conducted using the scientific method: developing a testable hypothesis and, hopefully, crafting well-devised experiments in order to interrogate the hypothesis. Open publication of methods and results, internal and external debate, and reproducibility of results are among the many ways in which a hypothesis will be tested over time, narrowing the results toward either a more or less trusted conclusion. The history of deep stops, and possibly to a lesser extent, that of pearl divers, share few, if any, of the rigors commonly associated with the scientific method.
Looking to the history of decompression research, the objective of a particular study is implicit, if not explicit, in the development and testing of a hypothesis. With decompression profiles, we seek to balance the safety of the majority while not unduly affecting the whole. For example, we seek ascent profiles that keep a high percentage of individuals from being injured while not greatly extending the decompression time of the group as a whole. What would the results look like if we instead sought the most efficient decompression for a select minority of individuals?
Some researchers joke among themselves that they already know who will get bent among a group of test individuals. This is because research trials require a lot of volunteers among a relatively small population of willing participants, meaning that some of the same individuals are often involved in multiple experiments. This is not to say that a few individuals have skewed all research, but rather to say that a minority of subjects in all research projects can affect the outcome by being particularly susceptible to decompression stress.
This individual susceptibility is likely no surprise to anyone and is relatively well established among researchers, as is the variability in one individual from one day to the next. We see such variability in almost every conceivable area of our lives, affecting the way we respond to everything from drugs and alcohol to food and criticism. How could it be otherwise? We are all a kind of genetic experiment, refined through time with an endless series of personal and species-wide successes and failures. If we are variably sensitive to decompression stress, as seems almost certain, then in what myriad of ways might that be playing out?
It appears that some individuals bubble more and some less on the same profile. Might they also be more or less sensitive to whatever collection of bubbles are generated? Is it possible that we develop different collections of symptoms to various types of decompression stress? That we are individually more or less sensitive to similar symptoms? Some of these factors we believe to be true and some we might suspect to be true. Many others lurk in the background, and all impact our sense of what we might call decompression stress.
Given a world filled with individuals, we must do our best to bridge the divide. The good news is that we do this relatively well seeing that some differences are important but most are not usually extreme. The tail of the distribution represented by a small number of resistant individuals may well be quite small. This means that building profiles for resistant individuals might not have much impact and/or might be unreasonably dangerous. Either way, this individual variability is highly relevant and holds promise for the future. The next big advancement in health care will likely involve personalized medicine. Most of us may not live to see the usefulness of these developments in medicine, much less in decompression research, but the process is nonetheless hopeful. For example, research on heart rate variability ( HRV ) might be one such development, allowing a theoretical computer to monitor your individual stress and adjust the ascent accordingly.
Managing individual susceptibility to a fluctuating range of variables is complicated, especially when many of these variables remain undiscovered, or at least poorly understood. Clearly, all is not lost, as we do a very good job managing the problem of decompression sickness. Depending upon our measure of success, we could say this problem is effectively solved. The fact that we are arguing about the nuances of decompression-stop arrangement and obsessing about relatively small adjustments to our total decompression time speaks to this success. We are likely refining along the margins beyond the point of diminishing returns. However, we should not fool ourselves into thinking that we have all the answers.
It’s The Data, Stupid
Another way to look at the science of decompression is to say it has mostly been a data-gathering exercise around which we fit slowly evolving boundary conditions. The boundary conditions are prescribed by algorithms and work quite well as long as we stay roughly within their range. It is quite possible we are not capturing any kind of truth about the way things work but rather refining our boundaries as we gather more data. It is true that we briefly foray into the field for some bubble-dynamics or that we strive to define the boundaries with process-markers like immune response, but none of these aspects has yet to produce a credible change in current practices.
By far the most useful part of decompression research has been the accumulation of data and the refinement of algorithms that capture these outcomes. Ideally, these algorithms would extend well beyond the data they describe, supporting “safe” diving profiles where sparse or even no data exists. Yet, evidence suggests that our models are especially bad in these outlier territories including very deep and/or very long dives. Most divers with meaningful experience in the 100+ meter range will admit they have little assurance of a clean ascent absent any symptoms of decompression sickness. These aspects further suggest that we are working in the proverbial dark, or at least just barely within the distant illumination of modern knowledge. This appears true at least with respect to specific determinations of cause (mistakes made) and effect (DCS incidence). Attempts to manage this uncertainty are in process among researchers spanning the globe.
Most experts are convinced that bubbles play a role in developing symptoms of decompression sickness, and most of these believe the effect is significant. In this regard, we have perhaps not come so far from Haldane or Buhlmann, who were both well aware of bubbles but lacked the tools to manage their development throughout a diver’s ascent. Likewise, the most recent deep stop studies do not propose that bubbles are irrelevant, only that deep stops appear inefficient and, in at least some cases, can increase risk. On the other side, we have evidence that slower ascents and/or deeper stops can reduce bubbling, but we remain unclear about the degree of importance the bubbling itself represents, especially over the long ascents conducted by technical divers.
Even a perfect model of bubbles might fail to predict or appreciably reduce decompression sickness, given the many complications in asserting the specific effect of bubbles in a given individual or within a particular injury. We are probably far from a perfect bubble model and perhaps even farther from determining how the wide array of variables might impact different individuals over time.
Perhaps we can find a way to manage our uncertainty while still progressing our understanding of the likelihood of a given outcome. For good reason, this process is reminiscent of mysteries coming to light in other fields. We seem to be discovering that more knowledge in a given area does not always result in a clearer understanding. Less than 50 years ago, most people were convinced we had “solved” the mystery of elementary particles, bundling the atom in nice packages of three constituents with simple-sounding names. Now the more we learn, the better we measure, the deeper we look, the more unsettling is the complexity.
Probabilistic Models and Uncertainty
Despite the confusing world around us, we have managed to achieve a high degree of success, and this continues despite our uncertainty. Management of this uncertainty can be mitigated by the use of probabilistic models and is currently common in other disciplines. This is an interesting and promising field, though it seems unlikely probabilistic decompression models will greatly change our current decompression profiles. This assumption may be wrong but seems appropriate, partly because we already have very low levels of decompression sickness, and partly because we have many supporting dives validating current time/depth profiles.
Adjustments like deep stops temporarily promised to reduce decompression time, perhaps by as much as one-third, but failed to materialize when tested more rigorously. This seems likely to remain true, at least as long as we assert a primary objective in maintaining very low DCS risk for the overwhelming majority. There may be a variety of small improvements to be found, but our current approach seems broadly “correct,” at least within the bounds of most active diving profiles.
In some ways, we already manage uncertainty but do so indirectly by assigning a very low level of acceptable risk to the profiles that we test. This ultimately impacts the resulting decompression schedule. Using probabilistic models might allow us to permit a high level of risk, which could conceivably shorten decompression time. However, it remains to be seen if these models will be released in a way that allows users to accept high levels of risk. Even if such options become available, I wonder how many divers would use them in an aggressive way. Regardless of these factors, probabilistic models might allow a rational selection of risk, especially for those with the requisite understanding.
Current and foreseeable models may not be describing any sort of truth, but they do appear good at determining useful boundaries (time and depth limitations) around which a desired outcome (limited DCS risk) appears most likely. I do not mean to belittle that success in the least. We maintain a high degree of confidence we will not suffer decompression sickness on most dives, and that is no small achievement. Yet, it also brings us full circle and back to the idea that modern-day decompression tables are largely determined by those most susceptible to decompression sickness.
The NEDU study was stopped when it reached a threshold relating to DCS outcome. In this case, 10 of 198 dives resulted in DCS symptoms. Most were mild, late onset, Type I, but with two cases of rapidly progressing CNS manifestations. Two of the DCS cases were experienced by one individual. Ethical considerations require that a manned diving trial with DCS as an end point be designed to limit unnecessary injury to divers by maintaining a low level of DCS risk. This is a sensible and inevitable outcome of human trials.
I am not advocating for a change to this strategy, but I am curious how this process affects our understanding of DCS, since we know little about the reactions occurring in more than 90 percent of test subjects. Would these individuals begin experiencing low-level symptoms after longer exposures? How much longer? Would we suddenly start seeing dangerous Type 2 symptoms in a rapidly escalating percentage of individuals? This rapidly escalating risk seems likely based upon experience with provocative profiles, but the details remain poorly defined.
Maybe some individuals are more resistant to bubble formation while they or others are less sensitive to the bubbles that form. We can find many cases of prolific bubbling absent DCS symptoms. Meanwhile, DCS symptoms can be present with no detectable bubbles. This is to be expected, as symptoms are at least partly related to where bubbles are located. But these results might also hint at other differences in our response to bubbling. What if some divers form bubbles easily and/or experience high susceptibility to any formed bubbles? How would that knowledge affect any decompression recommendations? Is it conceivable that what works well for one diver or even the majority of divers is not optimal for all divers?
All of this ambiguity should lead a thinking person to question the certainty of their pronouncements. We might be inclined to reduce our deep gradient and ascend more quickly from depth, as the developing evidence indicates. But we should also respect the dive buddy that says they get bent when moving quicker in deep water. We can’t definitively say what works best, but we can say what seems to work well in the majority of cases for the majority of people. For most divers, these debates are largely academic, since the differences in profiles amount to minutes in one direction or another.
Technical divers are progressively more affected by changes in recommended ascent profiles in relation to the length of their dives. Yet, even tech dives of relatively modest lengths show impacts of less than 10 minutes and are usually not worth nearly as much anxiety as one can find in the community. Having said this, it is easy to appreciate the desire to maximize efficiency. I am merely trying to suggest one should not be in a big hurry to change what seemed successful in the past. Those wishing to balance experience with evolving science might begin to raise their deeper gradients in a progressive fashion over time while paying attention to how they and their dive buddies respond. Or a person that perceives success with their current approach might choose to hold tight and make few, if any changes. I am arguing that we should recognize both opinions have merit and that we should take each perspective into account when working within our team to establish a given ascent schedule.
The one definitive thing we can say about decompression is that it works well in the vast majority of cases, and when it doesn’t work, we probably will not know the exact reason. That reality is unlikely to change in the foreseeable future, although we certainly need to keep trying. A knowledgeable friend of mine once said that if we get bent, it is because we did not do enough decompression. Truer words have never been spoken.
I am very curious to hear about your experiences and opinions regarding evolving decompression science. Are most of you convinced that deep stops bring no value? How many think they are dangerous? Do you think I make too much of individual susceptibility, or do you see that in your own experiences? I welcome all points of view, critical and otherwise. Let the games begin :-).
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.
Risk-Takers, Thrill-Seekers, Sensation-Seekers, and … You?
It’s likely that many in our community no longer think of tech diving as a risky activity, or perhaps even appreciate how important taking risks may be to one’s personal health—let alone that of our species. Fortunately, InDEPTH’s copy editing manager Pat Jablonski dived deep into the origins, meaning, and benefits of regularly taking risks, and even offers a thrill-seeking quiz for your edgy edification. What have you got to lose?
by Pat Jablonski. Title photo courtesy of Katelyn Compton Escott.
“Life without risk is not worth living.” – Charles Lindbergh
What defines a risk? What is involved in taking a risk?
Difficult questions to answer, because something that feels risky to one person might be yawn-worthy to another. Risk taking, unscientifically, is something you do that gets your blood up, raises your heartbeat, awakens your senses, and makes you hyper-aware of your surroundings.
Surely we can agree that the Covid pandemic has added an unexpected level of risk to everyday life. Add poor drivers, mass shootings, contentious politics, global climate change, and many are left believing that meeting each day is risky enough. But that’s not true for people who identify as risk-takers or thrill-seekers.
“Everyone has a ‘risk muscle’. You keep in shape by trying new things. If you don’t, it atrophies. Make a point of using it once a day.” – Roger Von Tech
There are many activities that go to the trouble of defining the level of risk involved with a specific activity, and while that’s not the purpose of this article, you should know that scuba diving ranks fairly high on the risky behavior scale–higher than skydiving and rappelling. And, cave/wreck diving or freediving isn’t on any risk scale we could locate. We can assume it’s up there—near or at the top.
Divers are a fairly small niche group for many reasons. One of them could involve the degree of danger associated with the sport. Answer this: Do dry land people ever ask you why you would want to take such a chance with your life in order to go where you weren’t meant to go?
It’s a reasonable question, albeit a hard one to answer.
“A life without risk is a life unlived, my friend.” – Big Time Rush
Kevin Costner’s Waterworld aside, humans have (yet) to be born with gills or webbed toes. Still, there you are. You’ve spent unmentionable amounts of money. You’ve carved out a whole day, or maybe weeks, away from your to-do list. You’re suited up and look like an alien. You’re on a quest to explore the aquatic world where you’re able to breathe only with a cumbersome apparatus. You’re planning to explore inner space! You’re going to delve into that amazing realm that’s off limits to most people.
You may look all matter-of-fact, cool as a cucumber, another day at the office, but it’s a thrill, isn’t it? Inside, you’re a kid with butterflies in your tummy who’s getting away with something big and exciting. Okay, it’s true–you and your team are highly trained, your equipment is top-notch, every box is checked off, and you are behaving responsibly. However, you’d have to be in a coma to not realize that what you’re about to do is taking a risk. Who doesn’t know that people have died doing what you’re doing? Answer honestly: How much more exhilarating is the experience when you know it’s not a walk in the park? Our own Michael Menduno admitted that “the feeling of being more alive lasted for days” after a dive.
So, you’re a diver. Does that mean you’re a risk taker? A thrill seeker? A sensation seeker?
Let’s dive into that subject, first by taking a little quiz, shall we?
From A Death Wish to Life Is Precious
In the past, too many mental health professionals treated risky behavior like a disease in need of a cure, focusing on the negative side of risk, even using government funding to address risky behavior and stamp it out.
Before that, Sigmund Freud might have even believed that thrill seekers had a death wish; in fact, it’s what was believed for many years.
Modern-day science doesn’t support either theory.
“Only those who will risk going too far can possibly find out how far one can go.” – TS Elliot
For our purposes, we’re focusing on the positive aspects of taking chances, pushing boundaries, and seeking experiences that make life feel . . . more alive. Richer. Fuller. We want to examine what goes into the psyche of a person (like you?) who is enthusiastically willing to engage in an activity already identified as dangerous, possibly even by the people who are engaging in it, and hear what some experts on the subject have to say about such people.
The University of Michigan’s Daniel Kruger proposes that taking chances is a fundamental part of human nature going all the way back to our ancient ancestors—prehistoric humans who had to constantly put their safety on the line in their fight for survival. Think fighting off a wooly mammoth with a stick. Kruger believes we have consequently retained many of those same instincts today, and he believes that it’s a good thing.
This writer, who is related to a major risk-taker, has always believed that heart-quickening experiences are essential for a well-lived life. I’m convinced and have long proposed that those pulse-pounding moments are often accompanied by a deepened understanding of and appreciation for one’s life—perhaps all life. And I’m happy to report that current science confirms that belief.
“If you are not willing to risk the unusual, you will have to settle for the ordinary.” – Jim Rohn
Dr. Kruger is one of the scientists who proposes that taking risks means “seeking that moment when life feels most precious.”
This should not be news for you diving adventurers out there.
Nature vs. Nurture: Born That Way or Learned To Love Adventure
Another scientist, Marvin Zuckerberg, affirms the theory that risk taking is in our DNA. “Certain people have high sensation-seeking personalities that demand challenges and seek out environments that most people’s brains are geared to avoid.” I’ll go out on a limb and say that underwater caves or shipwrecks would qualify as environments most would avoid.
Dr. Cynthia Thompson, the researcher behind a 2014 study from the University of British Columbia, was early to look at the genetic factors that might make a person predisposed to participating in extreme sports, ones that are typically defined as activities where death is a real possibility. The results of her study revealed that risk-takers shared a similar genetic constitution, a genetic variant that influences how powerful feelings are during intense situations.
Most scientists agree that personality is a complicated mix of genetic and environmental influences. The “nature vs. nurture” dilemma is alive and well. Dr. Thompson concluded that people who engaged in so-called high-risk sports were not impulsive at all, not reckless either. Instead, “they’re highly skilled masters of their discipline who take a very thoughtful approach to their sports.”
A study conducted in 2019 examined human boundaries, people who pushed them to their limits and beyond, and what made those people tick. Zuckerman labeled such people “sensation seekers” and defined them as “people who chase novel, complex, and intense sensations, who love experience for its own sake, and who may take risks to pursue those experiences.” Is that you?
“History is full of risk-takers. In fact, you could say that risk-takers are the ones who get to make history.” – Daniel Kruger
Other experts posit an alternate theory—one proposing that modern society in the age of seatbelts, guardrails, child-proof caps, safety precautions, laws, rules, and regulations has dulled the sense of survival. In other words, life has flattened out and no longer feels exciting, or risky. So, is one of the reasons we seek excitement because of boredom?
Maslow’s Theory of Self-actualization
I don’t honestly know who was the first proponent of risk-taking being a positive thing, but the work of Abraham Maslow, the founder of humanistic psychology, was one of the first. Maslow became one of the most influential psychologists of the twentieth century, and he developed a theory of human motivation that advocates for “peak experiences.” Peak experiences are not attained without risk.
“One can choose to go back toward safety or forward toward growth. Growth must be chosen again and again; fear must be overcome again and again” – A Maslow
He proposed that, in addition to meeting basic needs, all humans from birth seek fulfillment in terms of what he called self-actualization—finding their purpose/being authentic. Self-actualization involves peak experiences—those life-altering moments that take us outside ourselves, make us feel one with nature, and allow us to experience a sense of wonder and awe. Maslow also believed that those who were able to have such peak experiences tended to seek them out rather than waiting for the next random occurrence. Hence the anticipation of the next dive?
“Do one thing every day that scares you.” – Anonymous
Out of Your Comfort Zone Into A World of Wonder
Psychologist Eric Brymer from Queenstown University of Technology in Brisbane, Australia, has spent years studying extreme athletes and has this to say: “They’re actually extremely well-prepared, careful, intelligent, and thoughtful athletes with high levels of self-awareness and a deep knowledge of the environment and of the activity.”
Recent research backs up what some extreme sports athletes have been saying for years, even if only to themselves.
“What participants get from extreme sports is deeply transformational, a sense of connecting with a deep sense of self and being authentic, a powerful relationship with the natural world, a sense of freedom,” says Brymer. “They get a strong sense of living life to its fullest as if touching their full potential.”
Brymer’s comments mirror what Maslow, the founder of humanistic psychology, said back in the 1940s.
We’re not advocating for taking stupid chances (such as diving without proper training, or necessary precautions) and we don’t believe anyone reading this article does that. We simply intended to focus on the scientific evidence that supports adventurers—people who get a thrill from an activity that offers—as a bonus; a chance to feel awakened from the mundane and thrust into a world of wonder.
Risk-takers and sensation- or thrill-seekers chase unique experiences. Often, those experiences bring awareness of important issues or increase essential knowledge about the planet we share. Many people overanalyze and dither when faced with an unfamiliar situation; they shy away from unsettling circumstances. Risk-takers face the unknown and trust themselves to prevail. Learning to scuba dive, for example, pushes people out of their comfort zone, takes them into a realm foreign and mysterious. Diving forces divers to pay complete attention to a task, to focus with laser-like precision in order to conquer misgivings, and to attain a skill that few others have. Confidence comes with accomplishment. Leadership emerges. Fear is overcome.
Sensation-seekers see potential stressors as challenges to be met rather than threats that might defeat them. With action, resilience develops. High sensation-seekers report lower perceived stress, more positive emotions, and greater life satisfaction. Engaging in extreme activities brings them peace.
What does it bring you?
Bandolier: Risk of dying and sporting activities
National Geographic: What Makes Risk Takers Tempt Fate? Recent research suggests that genetic, environmental, and personal factors can make people take on risky—even potentially fatal—challenges.
Healthday: Taking Risks By Chris Woolston HealthDay Reporter
Pat Jablonski heads up the copy edit team for InDEPTH. She is a blogger, a writer of stories, a retired tutor, English writing teacher, and therapist. She’s a friend, a wife, a proud mother and grandmother. She is also a native of Florida, having spent most of her life in Palm Beach County. She has a B.A. in English from FAU in Boca Raton and an M.S.W. from Barry University in Miami. She learned to swim in the ocean, a place she thinks of as home, but she doesn’t dive.
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