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Incident Report: Knowing When To Thumb The Dive

Conducting an incident and accident analysis after the event is relatively easy. Incident and accident prevention, or risk management, is much harder to do because we don’t know which of the thousands of possibilities are the relevant ones.

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By Gareth Lock

“Success is a lousy teacher if you get it right the first time.”

Conducting an incident and accident analysis after the event is relatively easy. Incident and accident prevention, or risk management, is much harder to do because we don’t know which of the thousands of possibilities are the relevant ones. This is especially true with diving. As such, we have to be conscious of our own limitations (skills and experience) and the pressures we will face. Not just time pressures, but also the social pressures we are under.

If someone invites you on a dive that looks exciting, a dive with other divers whom you respect and admire, and they have invited you along because of a certain skill set you have, such as surveying, photography or videography, it can be very hard to execute the right (which every diver has) to thumb the dive at any time for any reason. This is often even harder when we start to look at previous dives that turned out alright, because success is a lousy teacher—especially if you get it right the first time.

Photo by David Rhea.

“In 2015 I was asked to join a project as a documentation diver that would collect photos and video on a dive. We were a relatively large team of eight divers sectioned into four two-diver teams. My teammate on the dive was also the dive equipment manager for the project. At this point, I was still new to diving doubles and did not yet have a doubles wing of my own. Instead, I used one of the wings provided to me, not knowing that it had previously been scheduled to be serviced before this project began.

As we discussed the dive plan to a depth of 100 ft/30 m in a heavy current, it became clear to me that I would have to dive beyond my limits to make this mission a success due to the increased video and lighting equipment, and the scooter they were mounted on. Immediately I realized that I had a choice to make: scrub the mission or push forward and accept the risk associated with adding extra gear to a working dive. To me, adding the equipment wouldn’t be too difficult to manage, but I also did not think far enough ahead to unforeseen issues.

We ran through our pre-dive checklist, the GUE EDGE, on the surface. Everything was good to go. We entered the water as a team and descended fairly quickly to avoid the current throwing us off our bearings on our way to the dive site. To maximize the bottom time, I was diving double AL80s, with an AL80 stage bottle to breathe enroute to the target area. To maximize time in the area, I was using an exploration-sized scooter/DPV that had a DSLR camera, video lights, and housing mounted to the nose. I felt a bit overloaded and my heart was racing, but after we hit the water and submerged, I began to calm down. We scootered downward and forward, which was relaxing and exhilarating at the same time.

This would be only my second scooter dive, my first with a camera mounted on it, and my first time managing a stage and switching regulators at depth. I felt confident in the scooter though, as my first ride went well and in this case it was helping to transport me and stabilize the camera. With the camera adding extra weight, the scooter was negative. This wasn’t really the issue I thought it would be. My confidence in using a stage was based on having filmed the required skills previously, with an instructor, and having watched it many times during editing process.

We stopped during the dive to check our bearings in about 80 ft/24 m of water. Being new to scooter diving, I thought it prudent to power it off while we were waiting to save battery life. At this point the scooter began sinking, so I decided to add a squirt of air into my wing to maintain neutral buoyancy. Shortly thereafter, the power inflator became stuck on as a result of corrosion built up after being in a salty environment for a year without proper maintenance.

My wing began to fill up and the inflator button was not responsive. Since this was my first experience of this, I did not immediately remember my training. However, muscle memory kicked in, and I first quickly signalled my teammate with a rapid light signal. He was looking right at me, so I figured he would be on his way over to help me, but he didn’t. I consequently began to manage the issue myself and reached back to dump the excess gas in the wing with my free left hand.

As I traced my hand back to find the dump valve to relieve excess gas from my wing, I found instead a stage bottle, which my mind said should not be there. I was able to get my hand around it and find the dongle to dump my full wing, but it continued to inflate. I tried to trigger the scooter to hold me at depth but I had turned it off. The thought process developed during training finally kicked in, and I unplugged the inflator hose. Luckily, the over-weighted DPV helped to hold me at depth long enough for me to manage this issue, and my buoyancy didn’t vary too much.

The rest of the dive was uneventful once I was stabilized in the water and had resolved the issue with the inflator hose.

Photo by Dickie Walls.

During the discussion after the dive, there were many lessons my team and I identified and subsequently learned:

  • My teammate never saw me signal, nor did he ever notice I was having trouble, highlighting the importance to both of us of situational awareness.
  • A quick tap of the inflator button to check for proper function during a pre-dive check is not adequate.
  • Overloading oneself with new gear, while easy enough to manage with good skills and the right mindset, can quickly become a serious inhibiting factor in an unexpected situation or when an emergency is encountered.
  • Poorly maintained gear, due to either an act of laziness, forgetfulness, or of being too burdened with other tasks to get the job completed, can cause problems!
  • The dive plan that revolved around me as the camera operator had requirements beyond my training or experience level.
  • I made a repeated series of misguided actions, like turning off the scooter or forgetting I had to get my hand around a stage, instead of immediately just disconnecting my power inflator hose. I had never had to do that before, but during the dive I remembered I saw my fundamentals instructor posing the question to us during class four years prior.

So the situation is all very clear to me now, and I can see how it could have been worse, but also how it could have been handled better. I learned from this experience. I now know better what my limits are and how I could misperceive the skills required versus my current skill levels. That day I became a better, safer diver because my mindset changed. I have continued to train and dive with a new mindset that will hopefully lead to me handling issues in a more intelligent way as I continue forward on project dives and into the beautiful world of cave diving.”


Photo by Andreas Hagberg.

Comments: The subject diver picked up many of the issues they personally faced. These included overconfidence, inadequate technical skills, assumptions, hubris, decision-making, and some of the factors associated with their teammate (I’ll comment on this in a moment). But there are also factors which were missed covering the wider project. Specifically, the team had an expectation that someone with limited experience would be able to pick up a complex task and manage it, even if something went wrong.

Executing this dive when everything was 100% perfect wouldn’t appear to have been an issue, but how often do we consider the “what ifs”—you can’t rely on everything being 100% perfect 100% of the time. As project leaders, how often do we consider the pressures to conform socially, which makes it harder for inexperienced but massively keen divers to say “this isn’t right” and thumb the dive or at least raise some concerns? The greater the social kudos associated with the project, the harder it is to say no.

The comment about the situational awareness of the teammate is also worthy of note because situational awareness is based on building up knowledge using your senses. Just because something is in a teammate’s field of view it doesn’t mean that they have seen it. The diver that had the problem had the responsibility to ensure that the communication loop with their teammate had been closed by signalling until the teammate responded, indicating that they were cognisant that the diver had an immediate problem.

Innovation and exploration cannot happen if you don’t push the limits. By definition, you are stepping outside the experience zone. This also means that the margins for error are greatly reduced and therefore there is a need to get everything as close to 100% perfect as possible. This requirement to “fail safely” means identifying interactions within the system that might cause you and your team problems, e.g., heavyweight scooter, additional stage, lack of practice, and what you can do to mitigate those risks from materializing.

The opportunity to learn directly from adverse events can be hard because diving is pretty safe (in terms of numbers). For that to happen, there needs to be a “just culture”. A just culture isn’t a blame-free culture, but one which recognizes that we are all human, that we all make mistakes, and that grossly negligent behaviors will not be tolerated.

With a just culture in place, we can learn from others by having context-rich stories like the one above, which look at not only the technical aspects (scooter weighting, OPV, servicing of the inflator) but also the human elements (skills practice, social pressures, inexperience, assumptions, hubris) so that we are better prepared to deal with the uncertainties and fastballs that come our way. Learn from your mistakes; better still, learn from someone else’s.

To learn more about “just culture” and what it can do for your team, follow the link to this free Human Diver webinar. Read Gareth’s post Mental Models to learn more about how our subconscious actions effect our safety.


Gareth Lock is an OC and CCR technical diver with the personal goal of improving divingsafety and diver performance by enhancing the knowledge, skills, and attitudes towards human factors in diving. Although based in the UK, he runs training and development courses across the globe as well as via his online portal https://www.thehumandiver.com.He is the Director of Risk Management for GUE and has been involved with the organization since 2006 when he completed his Fundamentals class.

Education

Part Two: “Tech Divers, Deep Stops, and the Coming Apocalypse”

In part two of this four-part series on the history and development of GUE’s decompression protocols, GUE founder and president Jarrod Jablonski discusses the lack of appropriate mixed gas decompression tables in the early days of technical diving. He goes on to discuss the initial development of “ratio decompression” and the early thinking and rapid adoption of “deep stops,” which have come under pressure as a result of new research that questions their efficacy and safety. He also discusses the emergence of the now nearly ubiquitous gradient factors (GF) used in most dive computing. Feel free to DIVE IN and share your thoughts.

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If you have not read Part One of the “Decompression, Deep Stops, and the Pursuit of Precision in a Complex World” series please find it here.

by Jarrod Jablonski

Header Photo by JP Bresser

Technical diving means different things to different people, opening legitimate arguments about different time periods and personalities involved in shaping this activity. Our purpose is more confined as I wish to focus mainly upon the development of decompression procedures. Leading figures like Jacques Cousteau (1910–1997) performed reasonably significant “technical” dives including both deep and overhead exposures. Yet, his dives were relatively short, often on air, and absent a community of fellow tech divers with whom to evolve varying strategies. Meanwhile, military or commercial activities reached significant depth with notable exposures but used different technologies and procedures. Hopefully, the following overview will be independently interesting—although I also hope to illustrate what I consider an intriguing wrinkle currently lacking in most debates over the best ascent schedule for a decompression dive.

For our purposes, I mark the 1980s as the period in which technical diving truly started to become a globally recognized activity. Of course, numerous significant projects occurred before this period, but the 1980s established a growing global awareness that amazing diving feats were possible by enthusiasts. The 1990s and the developing internet age brought these ideas progressively into the mainstream. Most importantly, these global communities could now easily communicate information and, of course, disagree about the best way to do one thing or another. 

Jarrod Jablonski, George Irvine, and Brent Scarabin preparing for dives in Wakulla Springs (late 1990s). Photo from the GUE archives.

The 1980s and 1990s were also an interesting period of development because people were doing more aggressive dives but still lacked important support tools that would take another decade to materialize. For example, most early tech dives were using some form of military, commercial, or scientific tables, such as the U.S. Navy, Oceaneering International, Inc. or the National Oceanic and Atmospheric Administration (NOAA), which were often not well-suited to the dive at hand. This is because there were no decompression programs available. Divers were unable to calculate their own profiles and would trade whatever tables they could gather. In many cases, they were forced to choose from tables that were calculated at a different depth, time, and/or breathing mix to the planned dive. 

George Irvine after a dive with the WKPP. Photo from the GUE archives.

Over time, the physiologist Dr. R.W. “Bill” Hamilton (1930–2011) began creating custom tables, but the lack of flexibility, as well as the cost, discouraged frequent use for most divers, especially when considering a range of depth profiles and their various time adjustments. This problem was especially prominent in deep cave diving where variable profiles and long bottom times created numerous complications . This landscape encouraged, if not demanded, that exploration divers be creative with their decompression practices. For example, Woodville Karst Plain Project (WKPP) explorers George Irvine and I began to explore ways to extrapolate from existing tables. The birth of what is now called ratio decompression originated with this practice. 

By exploring the way decompression schedules develop, we began outlining simple ratios that allowed divers to adjust their decompression based upon a ratio of time spent at depth. Then, in 1998, I went on to form Global Underwater Explorers (GUE), and such practices became part of the process for helping divers appreciate the structure of decompression while supporting adjustments to profiles when depth or time varied from that expected. Regrettably, some individuals took this too far and began promoting complex adjustments and marketed them as superior to the underlying algorithms from which they had been derived.

We should leave a more in-depth review of ratio deco for another time. For now, I intend to illustrate that “rules” such as ratio deco had their roots in limited availability of decompression tables and evolved as a useful tool for understanding and estimating decompression obligation. The fact that early tech divers had limited ability to calculate profiles encouraged a “test-and-see” philosophy, further fueling the early popularity of ad hoc adjustments to decompression profiles. This was most notable in the DIR and GUE communities through ratio-style adjustments and also prominent with non-DIR advocates who used a modification known as Pyle-stops, originating from ichthyologist Richard Pyle’s early deep dives and his attempts to refine efficient ascent protocols. One common adjustment in these approaches involved a notable reduction in ascent speed, adding additional stops known as “ deep stops

Driven by self-discovery, the migration toward deep stops resulted in rare agreement among technical divers, and the practice developed a life of its own in conference symposiums, being advocated far and wide by a healthy share of technical divers. The earliest phases of these modifications were driven in part by limited access to decompression tables, though by the end of the 1990s there were a variety of decompression programs available. This was a big improvement, although it was still true that divers had a limited baseline of successful dives while planning mixed-gas dives in the 50 to 100 meter range and beyond. Today, most divers take for granted that technical dives planned with available resources and within today’s common use (a few hours around 90m/300 ft) are relatively safe in terms of decompression risk. When these programs first came to market, there remained many question marks about their efficacy. 

Jarrod Jablonski and Todd Kincaid use Doppler while evaluating decompression profiles in 1995. Photo from the GUE archives.

The availability of decompression programs was a big advantage for technical divers, as they now had more sophisticated tools at their disposal. Yet, the output from many of these programs produced tables that were sometimes different to profiles thought to be successful by some groups. Typically, the difference related to an increase in the total decompression time and/or a distribution of stops that varied from developing consensus. These divers were keenly interested in the developing tools but reluctant to change from what appeared successful, especially when that change required additional hours in the water. A debate developed around the reason for these differences, bringing the already brewing interest in bubbles well into the mainstream. 

At the time, all tables were based upon dissolved gas models like Buhlmann, and thus not directly modeling bubble development during an ascent. Dissolved gas models preference ascents that maintain a reasonably high gradient between the gas in tissues and the gas being breathed, which should be supportive of efficient elimination from tissues. Dissolved gas models manage—but do not explicitly control for—bubbles and were thus labeled (probably unfairly) as “bend and mend” tables. In fact, dissolved gas models are designed to limit supersaturation (explicitly), because this is supposed to limit bubble formation. Haldane references this control of supersaturation in his pioneering publication .

Those advocating for different ascent protocols imagine that a lack of deep stops creates more bubbles, which then need to be managed during a longer series of shallow decompression stops. In this scenario, a slower ascent from depth, including “deep stops,” would reduce the formation and growth of bubbles while reducing time that might otherwise be needed to manage previously formed bubbles. Support for these ideas gained momentum in diving and professional communities, although some of these individuals were arguably conflicted by a vested interest in promoting deep stop models. Eventually, the practice received more critical consideration but during the intervening years deep stops were largely considered as common knowledge.

Jarrod Jablonski and George Irvine at the last stop of a 15-hour decompression in 1998. Photo from the GUE archives.

The idea of controlling bubbles became extremely popular through the 1990s, encouraging deeper stops designed to limit bubble formation and growth. The “test-and-see” approach developed by early tech divers appears to have fueled the promulgation of deep stops though the determining characteristics remained poorly defined. Early tech divers embraced the uncertainty of their activity, realized that nobody had the answers, and decided to “experiment” in search of their own answers. In fact, divers were experimenting with a lot more than deep stops, altering gases breathed, the placement of various decompression stops, and the total amount of decompression time utilized. This meant that divers were sometimes aggressively adjusting multiple factors simultaneously. 

For example, divers using a decompression program might input significantly less helium than was present in their breathing mixture. This was done because the algorithm increased decompression time with elevated helium percentage, sometimes known as the helium penalty . In other cases, divers would completely change the structure of stop times. For example, divers would invert the way a profile should be conducted by doing more time near a gas switch and less time prior to the next gas switch, believing the higher-oxygen gas only 3m/10ft away was time better utilized. 

I do not intend an exhaustive or detailed review but only to assert the many, sometimes radical approaches being taken by tech divers who often perceived success with these various strategies. In some cases, it appears these practices may have been leading the way toward improvements (eliminating the Helium penalty) while other adjustments might prove disadvantageous. In both cases, it is important to note that divers understood—or should have understood—these actions to be potentially dangerous, accepting risk as a natural part of pushing into uncertain territory where definitive guidance and clear borders are rarely available. 

None of this is to argue that divers should engage in aggressive decompression or challenge convention or place themselves at risk to unknown complications. I merely wish to clarify the atmosphere under which these adjustments were conducted, while highlighting that conventional ideas of risk mitigation are inherently complicated against a backdrop of novel exploration. A sense of relative risk dominated most of these trials since there are also risks associated with lengthy, in-water exposure. Eliminating what might be an avoidable decompression obligation could reduce risk from other obvious factors, including changing weather, dangerous marine life, being lost at sea, hypothermia, and oxygen exposure. Decompression experimentation was but one of many attempts to establish new protocols during extensive exploration projects. 

During this time, deep stops and similar adjustments were part of the “norm” for aggressive technical explorers who were sometimes notably reducing in-water time as compared to available tables. It is interesting to note that individual differences in susceptibility seemed among the most prominent variables across the range of tested adjustments, and we will return to this in a later discussion. For now, we should acknowledge that the “success” being achieved (or imagined) is greatly complicated by a small sample size of self-selected individuals who were simultaneously experimenting with a range of variables. On the other side, I do not want to entirely discount the results being seen by these divers. We should remember that development of safe decompression ascents for the general diving community was not the goal of most tech divers. These divers were interested in maximizing their personal and team efficiency during decompression. These strategies may or may not have been objectively successful or broadly applicable, but many teams imagined them so, at least within the narrow scope being considered. Later, we will return to these important distinctions with careful consideration for the potentially different interests being pursued by divers evaluating different decompression profiles.

Fortunately, a desire to create broadly useful tools was high on the list of priorities for some individuals in the technical diving community, leading to a relevant and important contribution. This inventive approach would introduce a new way to think about decompression, remaining to this day at the center of the debate about deep stops. 

Creating a New Baseline

Despite the popularity of deep stops and other modifications presented previously, technical divers lacked a common language for comparing the results, especially across different profiles. Compounding this problem was the variable way decompression programs considered a dive to be more or less “safe.” For example, some programs developed “safety factors” which increased total decompression time by an arbitrary factor, i.e., made them 10% longer. Other programs used different strategies, though it was not clear whether any of the various safety factors actually made the decompression safer. Whether safer or not, these factors were typically inconsistent and added complications when comparing various profiles. Just as these debates were reaching a fervor, help arrived from an unlikely place. An engineer by trade and decompression enthusiast by choice, Erik Baker had developed a novel solution. 

George Irvine passing time during a long decompression. Photo from the GUE archives.

Baker was seeking a way to establish consistency in considering the safety or lack of safety between various profiles. The term Baker applied was Gradient Factor (GF). I will not invest considerable time exploring the science behind GF, as many useful resources are widely available. For our purposes, it is sufficient to say that GFs allows a user to establish a lower threshold than the maximum recommended by a dissolved gas algorithm. This maximum pressure or M-value is assigned to “compartments” having an assumed amount of tolerance relative to the flow of blood they receive. Decompression theory is complicated by many factors but when the pressure of a gas in a compartment nears the M-value, it is thought that the risk of decompression sickness becomes higher. By adjusting a profile through the use of GF, one presumably reduces the risk. However, this also means there is less gradient between the gas in tissues and the gas in blood, reducing the driving force for the removal of gas and probably requiring additional decompression time. 

Gradient factors took an important step toward using a consistent language when talking about a variety of adjustments divers might make to their decompression. As part of his work on GF, Baker had developed a keen interest in the decompression adjustments by leading technical divers. Baker and I began working together while evaluating some of our most extreme diving profiles. This collaboration led to a number of productive developments including GUE’s DecoPlanner, released in 1997, and among the first to utilize GF methodology. These collaborations further highlighted what appeared to be a discrepancy between the decompression expected by dissolved gas algorithms and the decompressions being conducted by many technical divers. 

Decompression experimentation tended to cluster in small groups whose size was likely affected by self-selection with members who would stop or reduce aggressive dives when experiencing decompression sickness. Yet, it seemed possible that there was more to the story. These divers were doing several things that should have exposed them to notable risk and yet were repeatedly completing decompressions of more than 15 hours. Deep stops were only part of the story as these divers were ignoring conventional wisdom in several areas while notably reducing decompression time. What was behind this discrepancy? Were deep stops right or wrong? Was the conservative approach to helium right or wrong? Were these individuals lucky? Were they unusually resistant to decompression sickness, or were there other factors lurking in the background?

Note: I will outline many of these developments in the upcoming Part Three, where we more directly consider the modern challenges to deep stops and most especially the assertion they are dangerous. In the interim, I hope to hear from our readers. Do you have different experiences from this period? Do you think such experimentation is reckless or inadvisable? Please let us know your thoughts.


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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In this video, GUE President Jarrod Jablonski and Technical Administrator Richard Lundgren discuss some of the early hurdles associated with decompressing from deep tech and cave dives. This discussion explores the lack of readily available deep-diving tables and most especially those capable of managing multi-level profiles. They also explore the early development of ratio deco and similar “experiments” conducted by early technical divers.

What is Ratio Deco?

The basic idea of ratio deco involves establishing a ratio between the time spent at a given depth and the associated decompression. This is possible because the curve describing the relationship between bottom time and total stop time (TST) at a single depth can be approximated by a straight line. The straight-line approximation breaks down beyond a certain range but can be useful toward estimating decompression time. For example, the ratio in a typical tech dive at 45 m/ 150 ft using the appropriate gases is 1:1, meaning that a dive at 45 m/150 ft for 30 min will result in a decompression of 30 min while assuming appropriate bottom and decompression gasses.

We can also follow with adjustments for deeper dives so that each 3 m/10 ft deeper than planned would result in a decompression extension of five minutes. At some point the increase or decrease in the baseline parameter will break down, leading to profiles that are too conservative or too liberal and we need a new ratio such as the GUE standard for 75 m/250 ft at 2:1 where 30 minutes of bottom time results in 60 minutes of decompression, assuming appropriate decompression gasses arranged through a properly staged ascent.

What exactly are deep stops?

Deep stops are technically any stops added below what would otherwise be established by a typical dissolved gas model. Dissolved gas models establish faster ascents when compared to models that intend to reduce development of bubbles. Bubble-oriented models seek to reduce bubble development by ascending more slowly, usually by adding pauses or "deep stops".

“The formation of gas bubbles in the living body during or shortly
after decompression evidently depends on the fact that the partial
pressure of the gas or gases dissolved in the blood and tissues is in
excess of the external pressure. But it is a well-known fact that
liquids, and especially albuminous liquids such as blood, will hold gas
for long periods in a state of supersaturation, provided the super
saturation does not exceed a certain limit. In order to decompress
safely it is evidently necessary to prevent this limit being exceeded
before the end of decompression.”

Boycott AE, Damant GCC, Haldane JS. The prevention of compressed-air illness. J Hygiene (Lond ) 1908;8:342-443.

The extra decompression time calculated by various algorithms when breathing a helium mix is a consequence of the long held belief that helium, which is lighter than air, enjoys faster uptake by the body than nitrogen (in the case of the Buhlmann algorithm 2.65 times faster).

Compartments are hypothetical tissues which are intended to model how gas moves in and out of tissues where blood flow varies. Fast compartments are intended to model movement in a tissue with a lot of blood flow and slow compartments strive to model behavior in tissues with very little blood flow.