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Pulmonary Oxygen Toxicity: Expanding Our Understanding With Two New Models
Last September, InDepth presented new data-driven models to predict the risk of pulmonary oxygen toxicity on a dive, which arguably represent an advancement over the legacy REPEX method (OTUs). Now our resident dive geek Reilly Fogarty applies these models to predict and compare the risk results on two BIG tech dives: Italian explorer Massimo Bondone’s eight-hour jump to 199 m/650 ft on the SS Brandenberg near Tuscany, Italy, and Dr. Andy Pitkin’s 124m/404 ft deep, 12-hour runtime push dive at Weeki Wachee Springs, Florida. The results will get your lungs pumping!
By Reilly Fogarty
See Previous InDepth Story: How To Calculate the Risk Of Pulmonary Oxygen Toxicity by Ran Arieli
These days you would have to be a lunatic (J-valve fanatics, I’m looking at you) to dive without a pressure gauge. Without a gauge, you can’t know how much gas you have left: whether you’re riding the edge of your reserve supply or have enough gas to finish your dive and then some. Planning a dive without understanding oxygen toxicity risk calculations is just as dangerous, but a little more complicated to work through.
Unfortunately for new divers, there just aren’t enough synonyms for “glossing over” to illustrate the number of ways we avoid delving into the complicated science of pulmonary oxygen toxicity management via misdirection, well-meaning anecdotes, or junk science. Like many research theories, what we know about the physiology of the condition is still evolving. Simplified perspectives based on antiquated calculations have a way of initiating a cyclical pattern of compounding mistakes, as one diver explains their best understanding to another, with each diver adding some element of inaccuracy. Despite the challenges, it’s our job as divers to understand how and why we make the decisions that affect our safety.
No single article can hope to cover the scope of a topic like this, but our aim is to provide you with the necessary tools to begin to understand the physiology of pulmonary oxygen toxicity. Our modern understanding is closely intertwined with the history of research into the subject, so while our hope is to educate, we also want to avoid causing harm through misinformation or to give the false impression of complete understanding. Risk mitigation falls to you, as does comprehending the material before you attempt to apply it in your own diving.
The broad strokes of this research can be best understood through the evolution of the unit pulmonary toxicity dose (UPTD) model, the derived equation for repetitive exposure (REPEX) model, and modern approaches developed by Barbara Shykoff, PhD, and Ran Arieli, PhD. Much like the decompression models we use, these are largely (in some cases wholly) unproven models based on compounding theories. Interestingly, the oldest and most problematic of these methods remains the most-used and least frequently questioned by divers. Here’s what you need to know about pulmonary oxygen toxicity.
The Unit Pulmonary Toxic Dose (UPTD) Model
The UPTD model was first developed in 1970 by researchers at the University of Pennsylvania. The theory is based on the loss of vital capacity (VC – the maximum volume of gas that can be voluntarily moved into or out of the lungs) that the researchers believed correlated with the symptoms of pulmonary oxygen toxicity.
The researchers used a small sample group of young men to create a dataset on oxygen exposure symptoms. These participants were subjected to a range of oxygen exposures with PO2 ranging from 1.0 to 3.0 ATA over a variety of exposure durations from 3.5 to 24 hours. To compare exposures across PO2 and exposure time differences, a common unit was created—the UPTD. This unit was defined as the equivalent to one minute of exposure to 100% oxygen at one bar. UPTD could then be calculated as follows and exposures could be compared:
By converting exposures to a common unit, the researchers believed that dives could be compared across depth and gas choices, and repetitive dives could be compared by the sum of their exposure values.
Shortly after the initial work was published, the cumulative pulmonary toxic dose (CPTD) model was created to allow for continuous oxygen exposures above a PO2 of 0.5 ATA to be calculated and expressed in UPTD. As a result of this work, a rudimentary understanding of the onset and presentation of pulmonary oxygen toxicity symptoms began to evolve. It’s important to note, however, that the original UPTD model did not differentiate between dives performed one hour or 23 hours apart—there was no calculation for complete or partial recovery.
UPTD is now often shortened to oxygen toxicity units (OTUs) and the calculations are still widely used even 45 years after their development. It remains unclear whether the model is accurate or the results of UPTD calculations merely overlap adequately with safe limits under common diving conditions, but experts are increasingly finding fault with the model.
Notably, Barbara Shykoff, PhD and US Navy Experimental Diving Unit (NEDU) researcher, has cited several past works from Duke University, Clark, Lambertsen, and others in critique of UPTD applications in the real world. Among her complaints are several significant deviations from the model’s predictions among dives performed at PO2 other than 2 ATA, differences in underlying lung injury and physiology, and disparity between VC changes at mild and extreme PO2 exposures. Research from Clark and Lambertsen has also indicated that the “unit dose” concept may not be applicable in a linear fashion above a PO2 of 1.5 ATA, but requires calculation as a “function of time squared for higher PO2s”.
The Derived Equation for Repetitive Exposure (REPEX) Model
If UPTD was a best-fit model designed for a small data set, the NOAA REPEX model took that applied theory a step further. Developed by R.W. “Bill” Hamilton, PhD, in the early 1980s, the NOAA-derived equation for repetitive exposure (REPEX) model was designed to facilitate recovery and multi-day diving calculations. The model was notably never validated in divers but was built on the concepts of the original UPTD and CPTD model and other supporting studies.
Hamilton’s team set theoretical limits for various exposures, with 850 OTU being an allowable single day exposure but gradually reducing the average daily OTU as missions became longer. He did note that these exposure limit curves would have to be modified with operational experience or desired conservatism, but did not verify the curves with real-world trials. The most often-voiced concern about this model is that it is based on a linear extrapolation of prior data, data that may itself not be accurate. This leaves it with a number of significant flaws and potentially erroneous results, particularly outside the relatively narrow range of exposures for which the UPTD system was designed.
Supporters of the REPEX system might dispute those assertions. It is fair to point out that the NOAA oxygen exposure limit tables have been used extensively for several decades with a great deal of success. This success could be due to accuracy of the model within the applied parameters common in recreational diving. It could also be the result of significant conservatism caused by a large gap between the calculated limits and the real-world exposure limits that incur pulmonary toxicity risk.
Shykoff’s Calculator for Estimating the Risk of Pulmonary Oxygen Toxicity
Shykoff’s work is one of the first notable evolutions in the way we proposed methods to calculate pulmonary oxygen toxicity risk in decades. In a paper published in 2015, she outlines a method by which divers can calculate risk over the course of repeated dives. The method is centered around what Shykoff calls a “incidence-time model” that stipulates a linear relationship in a mid-range exposure value. This makes it possible to not only calculate oxygen toxicity for duration, but also extrapolate equivalent exposure time between exposures at different PO2s. This is coupled with a recovery model and centered around the idea that any dive with a PO2 of 1.3 to 1.4 bar begins some level of pulmonary injury. Shykoff admits that the probability of noticeable injury in small exposures is quite small, but she believes there is a proportional risk between this and intermediate duration exposures. This differs from the UPTD and REPEX models in that it significantly limits its extrapolation of linear relationships only to the intermediate exposures, notable because exposures beyond a small midrange have indicated significant variance from the norm in prior models.
Also important is the verification of Shykoff’s model. While its design relies on a relatively small dataset of 1350 in-water dives, the fact that it has been verified in divers at all separates it from its predecessors. These dives occurred with a PO2 of between 1.3 and 1.4 bar, and were used to create and verify the time-incidence model. An additional dataset using 620 dives was used to validate the recovery model used in Shykoff’s risk calculator.
After resting dives: ▲ / After dives with exercise: ■
The lines are the best fit models fitted to the data:
–––– for resting dives / – – – for dives with exercise,
tr/Tdur = exp[–k (t/Tdur)2], k = 0.149, 0.047 for resting dives or those with exercise, respectively.
Graphic courtesy of Babara Shykoff.
Interestingly, these data showed that significant recovery did not occur until nearly five hours after a dive, with no measurable recovery apparent after two separate three-hour dives that occurred with a two-hour surface interval between them. Whether this is a function of actual recovery mechanisms or a limitation of the model remains unclear.
In terms of practical application, Shykoff’s model makes a few interesting points. Most notably, she suggests completing shorter dives before longer ones, and a resting dive before one with exercise. This is both to avoid a possibly over-conservative calculation of risk due to the rate of recovery being calculated with the duration of exposure in the denominator, and because recovery after a dive that involves exercise occurs at nearly half the rate as one done at rest. It’s also important to note that zero incidence does not correlate with zero duration. Shykoff cites a 95% confidence limit for this model at 0.8 – 4.9%, meaning that—purely by the numbers—approximately 3% of divers in the model may exhibit signs or symptoms of pulmonary oxygen toxicity at the beginning of the dive with no exposure to elevated PO2. This point must be followed with the note that this is directly comparable to the overall incidence of symptoms found in a dataset of 239 shallow open-water dives with a PO2 of 0.3 bar (resulting in about 6% symptom incidence) and can be “interpreted as the effect of breathing underwater.”
Another key differentiation from prior models is the recovery rate calculation. While prior models used a first-order kinetic model, Shykoff used a sigmoidal shape recovery pattern based on real-world data. This means that recovery rates vary between their initial rate, a maximum rate, and a final slower rate in a non-linear fashion. More complex calculations alone don’t imply superiority, but Shykoff does have some real-word data to back up her model. Experimentally, it appears that injuries from one exposure may begin to diminish even as damage from a following dive occurs, leading to occasional improvement of symptoms in subjects who began a dive with symptoms (note that this is an experimental observation and NOT a recommendation or suggestion of causation).
This model also does not associate severity of oxygen toxicity with exposure duration. It also does not differentiate between severity of exercise, other effects of mild hyperoxia, or PO2 significantly deviating from 1.3 bar or beyond a single exposure of up to eight hours. The model is based on a small dataset, and its results should be treated as almost entirely theoretical in their current form.
Arieli’s Toxicity Index Derived from the Power Equation
Ran Arieli, PhD is the former head of Hyperbaric Physiology Research at the Israel Naval Medical Institute, and takes many of the same issues with the UPTD and REPEX models that Shykoff and their colleagues do. In response, he’s developed a method that focuses on a power-law approach to pulmonary oxygen toxicity risk calculations. This model focuses on the polynomial expression of reactive oxygen and nitrogen species that can be correlated with pulmonary injury, and the assumption that the development of these species is related to the highest power of the PO2 exposure. Combining this with other oxygen toxicity symptoms (decrease in lung capacity, ventilatory drive, or thickness of alveolar wall, for example) modeled by their exposure time, the rate of hydrogen peroxide (a reactive oxygen and nitrogen species precursor) can correlate with the square of time and—Arieli believes—can provide an ability to predict oxygen toxicity risk.
More on how Arieli derived his power equation can be found in a previous InDepth article, “How To Calculate the Risk Of Pulmonary Oxygen Toxicity,” but at its core his model was designed to address a demonstrable difference in pulmonary pathologies found at high and low PO2 exposures. Modeling different risk factors for each resulted in a model that Arieli believes more accurately represents pulmonary oxygen toxicity risk.
This model has the added benefit of being directly verifiable through the measurement of reactive oxygen and nitrogen species, or their precursors. The caveat to this is a correlation between these species, and the expected pulmonary pathology must be assumed, although these relationships are relatively well accepted. Like Shykoff’s model, Arieli’s proposed model has fairly specific parameters. Its initial publication specifically focuses on interpolating risk for exposures done under sedentary to light intensity activity (1 to 4.4 MET) in subjects either dry or immersed in 33°C water. The result is a model which Arieli believes can accurately be used to estimate pulmonary oxygen toxicity risk in divers but which must be carefully applied within the parameters of its original intent.
Applying The Models to Real World Dives
The SS Brandenberg
It’s hard to bring concepts like these into focus without crunching some numbers, so working through an example of a long CCR dive can help illustrate the differences. Take a dive like Massimo Bondone’s exploration of the SS Brandenburg for example. A British steamship torpedoed on February 10th, 1941, the Brandenburg now sits in nearly 199 m/650 ft off the coast of Tuscany, Italy. The Italian explorer and his team identified and dived the wreck in 2017. Their efforts represent the fourth deepest shipwreck exploration dive conducted by tech divers.
Using a closed-circuit rebreather Bondone logged 15 minutes of bottom time and a 490 minute total run time for his dive. This dive is extreme, and difficult to do without significantly exceeding CNS toxicity limits under almost all guidelines, but useful for exploring the limits of pulmonary toxicity which take greater total exposure time to exceed. Assuming a constant PO2 of 1.0 bar, here’s how each of the models works out:
UPTD:
Total toxicity in UPTD can be calculated as follows:
UPTD = t * [(PO2 – 0.5)/(1-0.5)]1/1.2
UPTD = (490 minutes) * [1.0 – 0.5)/(1-0.5)]1/1.2
UPTD = 490
This exceeds the latest US Navy Diving Manual limit for a daily exposure (450 UPTD), although a single extreme exposure limit of 1425 UPTD is designated for medical applications in the operational theater. Bondone’s dive was extreme, but UPTD guidelines put it just beyond the allowable limits for single-day pulmonary oxygen toxicity exposure.
REPEX:
That same dive by REPEX guidelines results in the same unit value – 490 OTU – but has significantly shorter maximum exposure durations.
By these guidelines, a 490 minute exposure to a PO2 of 1.0 bar is more than two hours over the limit for single exposures. There is no way to quantify the increase in risk once the limit is exceeded; the guidelines were designed to be binary. It is interesting to note how much shorter than the UPTD guidelines the REPEX exposure limits are.
Shykoff’s Method:
The Shykoff method is significantly more involved to calculate by hand, but is available to easily calculate via an online tool Shykoff has published. One issue with calculating this example dive, however, is that the model has been designed only for a PO2 range of 1.3 to 1.4 bar – the lower PO2 ranges commonly used for dives like this fall outside the intended range of the model. Calculating the dive with a higher PO2 but an identical dive time (something that might occur with more conservative gradient factors, for example) gives the following:
Unlike the older models, this calculation gives a probability of symptoms, rather than just a binary judgement on whether the dive fits within acceptable parameters or not. That probability does not imply accuracy in and of itself, but if the mode proves accurate it could provide new possibilities for dive planning in extreme exposures.
Arieli’s Method
Calculating toxicity risk by the power equation derived index method that Arieli has published requires a bit of work. For PO2 greater than 0.6 bar, the following equation results in the POT index:
POT Index = T2* PO24.57
This yields a POT Index of 49. This value can then be used to estimate incidence of toxicity symptoms via the following:
Incidence (%) = 1.85 + 1.071 * POT Index
This value, as estimated by the model and the dataset from 16 HBO exposures performed at the NEDU, results in an estimated 54% likelihood of pulmonary toxicity symptom evolution. Within the limitations of Arieli’s dataset, the predictions appear to have a strong correlation to real-world results, and the calculated risk is similar to that found using Shykoff’s model. Bondone reported that though he has had pulmonary oxygen toxicity symptoms on dives, he did not experience any symptoms after diving the Brandenberg.
Weeki Wachee
Pulmonary oxygen toxicity comes to the forefront of diver’s concerns as their expeditions grow longer, so there’s value in looking at a longer, slightly shallower dive as well. Dr. Andy Pitkin is a pediatric cardiac anesthesiologist and researcher who regularly participates in dives exploring some of the deepest caves in the United States. In 2019, he and his teammates performed a dive to a maximum depth of 124 m/404 ft in just over 12 hours while exploring the Weeki Wachee Springs system with the Karst Underwater Research (KUR) group.
The dive involved years of work-up and an innovative array of support personnel, equipment, underwater habitats, and emergency planning, but it’s the effect of the extreme exposure to elevated PO2 that we’re interested in here. Using a rebreather with a setpoint of 1.1 bar, Pitkin spent 725 minutes underwater. Ignoring the air breaks used to manage CNS toxicity near the end of his profile, here’s how each model breaks it down:
UPTD:
Here’s how Pitkin’s dive looks calculated via the original UPTD algorithm:
UPTD = t * [(PO2 – 0.5)/(1-0.5)]1/1.2
UPTD = (725 minutes) * [1.1 – 0.5)/(1-0.5)]1/1.2
UPTD = 843
Like Bondone’s dive, this exceeds the US Navy Diving Manual limit for daily exposure, this time by almost double (450 UPTD vs 843 UPTD). However, the allowable limit for a single extreme exposure of 1425 renders this technically within some limits, although those were intended only for medical applications in emergency situations. By UPTD standards, this dive would be significantly beyond any reasonable single-dive exposure.
REPEX:
Just as with Bondone’s dive, the REPEX calculations provide the same 843 OTU value as the UPTD calculations. In this case, the exposure is even further past the NOAA Diving Manual guidelines for a maximum single exposure (just 240 minutes at the working PO2 of 1.1 bar). It would not be possible to perform this dive via either REPEX or UPTD guidelines.
Shykoff’s Method:
It’s impossible to calculate this dive within the confines of Shykoff’s method because she designed her model around a working PO2 of 1.3 to 1.4 bar. Attempting to calculate a dive this long at an artificially high PO2 results in dramatic numbers, but none that reflect reality. Because Pitkin chose to run a lower PO2 to attenuate the risk of CNS oxygen toxicity, this dive falls below the more common working PO2 used by rebreather divers around which Shykoff has designed her model.
Arieli’s Method
This dive falls significantly beyond the exposure guidelines that Arieli has set forth, but his are less binary than those used by Shykoff’s model. Calculating POT Index as follows:
POT Index = T2* PO24.57
And theoretical incidence via:
Incidence (%) = 1.85 + 1.071 * POT Index
Results in a value of 240%, or 240% likelihood of pulmonary toxicity symptom evolution.
It’s results such as these that illustrate the fact that these models are entirely theoretical to those who are first playing with the data. Particularly as exposures deviate from the norm, their results will appear increasingly extraordinary, but none of those results may reflect reality in the first place.
Pitkin completed his dives with minimal symptoms, despite all four of these models indicating that it could be extremely hazardous to use such a profile. Pitkin explained that he and his partners frequently experience some low-grade symptoms of pulmonary oxygen toxicity following similar dives. These symptoms typically include “substernal tightness, mild cough, and the feeling of inability to take a deep breath,” which is why they now limit the PO2s on these dives. Symptom onset has become an expectation on dives such as these but severity is decreased by using a setpoint of 1.2 bar or less (interestingly, according to Pitkin, time to symptom onset is not improved by this change). “A bonus is you don’t feel as crappy afterwards,” he said.
Each of these four models has indicated the likely onset of pulmonary toxicity symptoms from this profile, and while symptoms have occurred they are perhaps milder than some models would suggest. This somewhat mixed result is indicative of the confusing nature of this type of modeling – Pitkin noted that, “there is a lot of inter-individual variation in susceptibility to pulmonary oxygen toxicity,” and this variability likely presents enormous challenges to accurate risk modeling.
We conferred with Arieli regarding these results. He noted that some recent research indicates the possibility of acclimatization to high PO2 exposures in technical and CCR divers that could explain lower than expected rates of CNS oxygen toxicity. This could potentially apply to pulmonary toxicity events as well.
Takeaways
The difficulty with covering a topic like this is the desire to educate but not instill undue confidence in divers. Knowledge is a powerful thing, and it’s easy to see research that agrees with what we’ve been taught and immediately apply it to our own diving. My hope is that you can take this article, use it to fill in the gaps in your own knowledge, and find the areas where you’d like to dig a little deeper.
UPTD and REPEX models may be inaccurate (wildly so in some applications), but many divers have been trained to use them in ways that promote safe diving practices and result in low injury incidence. Similarly, Shykoff and Arieli’s methods are exciting and appear accurate but lack the real-world testing to verify their efficacy. They are significantly hindered by their parameters, and we have yet to determine if they represent a more accurate model at large, or just a closer correlation to a limited dataset.
Like many elements of diving research, the potential here is enormous. While you may be left waiting for more research before you can change the way you plan your dives, it’s likely that these two models and those that will come from them will dictate how we dive in the future. Knowing how we got to this point, what the pitfalls of our current calculations are, and how researchers hope to remedy those pitfalls in the future is valuable and can contribute to your safety. Dig into the details wherever possible, see how each model calculates your most challenging dives, and think about how you can make your dives safer with all of the knowledge available to you.
A Special Thanks to Massimo Bondone and Dr. Andy Pitkin for sharing their dive data and Neal Pollock, Ph.D. for lending his expertise.
Dive Deeper:
InDepth: How To Calculate the Risk Of Pulmonary Oxygen Toxicity by Ran Arieli
Frontiers in Physiology: Aviner B., Arieli R.,Yalov A. Power equation for predicting the risk of central nervous system oxygen toxicity at rest
Arieli R., Aviner B. Acclimatization and deacclimatization to oxygen: determining exposure limits to avoid cns o2 toxicity in active diving
Calculator For Estimating The Risk Of Pulmonary Oxygen Toxicity by Dr. Barbara Shykoff
Shearwater Research: Why UPTD Calculations Should Not Be Used by Barbara Shykoff, 2017
Spums Journal: Tolerating Oxygen Exposure by RW Bill Hamilton, 1997
RW Bill Hamilton’s Original REPEX paper: Tolerating Exposure To High Oxygen Levels: Repex And Other Methods by RW Hamilton, 1989An early 1985 review of the UPTD Model: Predicting Pulmonary O2 Toxicity: A New Look at the Unit Pulmonary Toxicity Dose by AL Harabin, L.D. Homer, PK Weathersby and ET Flynn
Reilly Fogarty is an expert in diving safety, hyperbaric research, and risk management. Recent work has included research at the Duke Center for Hyperbaric Medicine and Environmental Physiology, risk management program creation at Divers Alert Network, and emergency simulation training for Harvard Medical School. A USCG licensed captain, he can most often be found running technical charters and teaching rebreather diving in Gloucester, Massachusetts.
Community
Twenty-five Years in the Pursuit of Excellence – The Evolution and Future of GUE
Founder and president Jarrod Jablonski describes his more than a quarter of a century long quest to promote excellence in technical diving.
by Jarrod Jablonski. Images courtesy of J. Jablonski and GUE unless noted.
The most difficult challenges we confront in our lives are the most formative and are instrumental in shaping the person we become. When I founded Global Underwater Explorers (GUE), the younger version of myself could not have foreseen all the challenges I would face, but equally true is that he would not have known the joy, the cherished relationships, the sense of purpose, the rich adventures, the humbling expressions of appreciation from those impacted, or the satisfaction of seeing the organization evolve and reshape our industry. Many kindred souls and extraordinary events have shaped these last 25 years, and an annotated chronology of GUE is included in this issue of InDEPTH. This timeline, however, will fail to capture the heart behind the creation of GUE, it will miss the passionate determination currently directing GUE, or the committed dedication ready to guide the next 25 years.
I don’t remember a time that I was not in, around, and under the water. Having learned to swim before I could walk, my mother helped infuse a deep connection to the aquatic world. I was scuba certified in South Florida with my father, and promptly took all our gear to North Florida where I became a dive instructor at the University of Florida. It was then that I began my infatuation with cave diving. I was in the perfect place for it, and my insatiable curiosity was multiplied while exploring new environments. I found myself with a strong desire to visit unique and hard-to-reach places, be they far inside a cave or deep within the ocean.
My enthusiasm for learning was pressed into service as an educator, and I became enamored with sharing these special environments. Along with this desire to share the beauty and uniqueness of underwater caves was a focused wish to assist people in acquiring the skills I could see they needed to support their personal diving goals. It could be said that these early experiences were the seeds that would germinate, grow, mature, and bloom into the organizing principles for GUE.
The Pre-GUE Years
Before jumping into the formational days of GUE, allow me to help you visualize the environment that was the incubator for the idea that became GUE’s reality. By the mid-1990s, I was deeply involved in a variety of exploration activities and had been striving to refine my own teaching capacity alongside this growing obsession for exploratory diving. While teaching my open water students, I was in the habit of practicing to refine my own trim and buoyancy, noticing that the students quickly progressed and were mostly able to copy my position in the water. Rather than jump immediately into the skills that were prescribed, I started to take more time to refine their comfort and general competency. This subtle shift made a world of difference in the training outcomes, creating impressive divers with only slightly more time and a shift in focus. In fact, the local dive boats would often stare in disbelief when told these divers were freshly certified, saying they looked better than most open water instructors!
By this point in my career, I could see the problems I was confronting were more systemic and less individualistic. In retrospect, it seemed obvious that key principles had been missing in both my recreational and technical education, not to mention the instructor training I received. The lack of basic skill refinement seemed to occur at all levels of training, from the beginner to the advanced diver. Core skills like buoyancy or in-water control were mainly left for divers to figure out on their own and almost nobody had a meaningful emphasis on efficient movement in the water. It was nearly unheard of to fail people in scuba diving, and even delaying certification for people with weak skills was very unusual. This remains all too common to this day, but I believe GUE has shifted the focus in important ways, encouraging people to think of certification more as a process and less as a right granted to them because they paid for training.
The weakness in skill refinement during dive training was further amplified by little-to-no training in how to handle problems when they developed while diving, as they always do. In those days, even technical/cave training had very little in the way of realistic training in problem resolution. The rare practice of failures was deeply disconnected from reality. For example, there was almost no realistic scenario training for things like a failed regulator or light. What little practice there was wasn’t integrated into the actual dive and seemed largely useless in preparing for real problems. I began testing some of my students with mock equipment failures, and I was shocked at how poorly even the best students performed. They were able to quickly develop the needed skills, but seeing how badly most handled their first attempts left me troubled about the response of most certified divers should they experience problems while diving, as they inevitably would.
Diving Fatalities
Meanwhile, I was surrounded by a continual progression of diving fatalities, and most appeared entirely preventable. The loss of dear friends and close associates had a deep impact on my view of dive training and especially on the procedures being emphasized at that time within the community. The industry, in those early days, was wholly focused on deep air and solo diving. However, alarmingly lacking were clear bottle marking or gas switching protocols. It seemed to me to be no coincidence that diver after diver lost their lives simply because they breathed the wrong bottle at depth. Many others died mysteriously during solo dives or while deep diving with air.
One of the more impactful fatalities was Bob McGuire, who was a drill sergeant, friend, and occasional dive buddy. He was normally very careful and focused. One day a small problem with one regulator caused him to switch regulators before getting in the water. He was using a system that used color-coded regulators to identify the gas breathed. When switching the broken regulator, he either did not remember or did not have an appropriately colored regulator. This small mistake cost him his life. I clearly remember turning that one around in my head quite a bit. Something that trivial should not result in the loss of a life.
Also disturbing was the double fatality of good friends, Chris and Chrissy Rouse, who lost their lives while diving a German U-boat in 70 m/230 ft of water off the coast of New Jersey. I remember, as if the conversation with Chris were yesterday, asking him not to use air and even offering to support the cost as a counter to his argument about the cost of helium. And the tragedies continued: The loss of one of my closest friends Sherwood Schille, the death of my friend Steve Berman who lived next to me and with whom I had dived hundreds of times, the shock of losing pioneering explorer Sheck Exley, the regular stream of tech divers, and the half dozen body recoveries I made over only a couple years, which not only saddened me greatly, but also made me angry. Clearly, a radically different approach was needed.
Learning to Explore
Meanwhile, my own exploration activities were expanding rapidly. Our teams were seeking every opportunity to grow their capability while reducing unnecessary risk. To that end, we ceased deep air diving and instituted a series of common protocols with standardized equipment configurations, both of which showed great promise in expanding safety, efficiency, and comfort. We got a lot of things wrong and experienced enough near misses to keep us sharp and in search of continual improvement.
But we looked carefully at every aspect of our diving, seeking ways to advance safety, efficiency, and all-around competency while focusing plenty of attention into the uncommon practice of large-scale, team diving, utilizing setup dives, safety divers, and inwater support. We developed diver propulsion vehicle (DPV) towing techniques, which is something that had not been done previously. We mostly ignored and then rewrote CNS oxygen toxicity calculations, developed novel strategies for calculating decompression time, and created and refined standard procedures for everything from bottle switching to equipment configurations. Many of these developments arose from simple necessity. There were no available decompression programs and no decompression tables available for the dives we were doing. Commonly used calculations designed to reduce the risk of oxygen toxicity were useless to our teams, because even our more casual dives were 10, 20, or even 30 times the allowable limit. The industry today takes most of this for granted, but in the early days of technical diving, we had very few tools, save a deep motivation to go where no one had gone before.
Many of these adventures included friends in the Woodville Karst Plain Project (WKPP), where I refined policies within the team and most directly with longtime dive buddy George Irvine. This “Doing it Right” (DIR) approach sought to create a more expansive system than Hogarthian diving, which itself had been born in the early years of the WKPP and was named after William Hogarth Main, a friend and frequent dive buddy of the time. By this point, I had been writing about and expanding upon Hogarthian diving for many years. More and more of the ideas we wanted to develop were not Bill Main’s priorities and lumping them into his namesake became impractical, especially given all the debate within the community over what was and was not Hogarthian.
A similar move from DIR occurred some years later when GUE stepped away from the circular debates that sought to explain DIR and embraced a GUE configuration with standard protocols, something entirely within our scope to define.
These accumulating events reached critical mass in 1998. I had experienced strong resistance to any form of standardization, even having been asked to join a special meeting of the board of directors (BOD) for a prominent cave diving agency. Their intention was to discourage me from using any form of standard configuration, claiming that students should be allowed to do whatever they “felt’ was best. It was disconcerting for me, as a young instructor, to be challenged by pioneers in the sport; nevertheless, I couldn’t agree with the edict that someone who was doing something for the first time should be tasked with determining how it should be done.
This sort of discussion was common, but the final straw occurred when I was approached by the head of a technical diving agency, an organization for which I had taught for many years. I was informed that he considered it a violation of standards not to teach air to a depth of at least 57 m/190 ft. This same individual told me that I had to stop using MOD bottle markings and fall in line with the other practices endorsed by his agency. Push had finally come to shove, and I set out to legitimize the training methods and dive protocols that had been incubating in my mind and refined with our teams over the previous decade. Years of trial and many errors while operating in dynamic and challenging environments were helping us to identify what practices were most successful in support of excellence, safety, and enjoyment.
Forming GUE
Forming GUE as a non-profit company was intended to neutralize the profit motivations that appeared to plague other agencies. We hoped to remove the incentive to train—and certify—the greatest number of divers as quickly as possible because it seemed at odds with ensuring comfortable and capable divers. The absence of a profit motive complemented the aspirational plans that longtime friend Todd Kincaid and I had dreamed of. We imagined a global organization that would facilitate the efforts of underwater explorers while supporting scientific research and conservation initiatives.
I hoped to create an agency that placed most of the revenue in the hands of fully engaged and enthusiastic instructors, allowing them the chance to earn a good living and become professionals who might stay within the industry over many years. Of course, that required forgoing the personal benefit of ownership and reduced the revenue available to the agency, braking its growth and complicating expansion plans. This not only slowed growth but provided huge challenges in developing a proper support network while creating the agency I envisioned. There were years of stressful days and nights because of the need to forgo compensation and the deep dependance upon generous volunteers who had to fit GUE into their busy lives. If it were not for these individuals and our loyal members, we would likely never have been successful. Volunteer support and GUE membership have been and remain critical to the growing success of our agency. If you are now or have ever been a volunteer or GUE member, your contribution is a significant part of our success, and we thank you.
The challenges of the early years gave way to steady progress—always slower than desired, with ups and downs, but progress, nonetheless. Some challenges were not obvious at the outset. For example, many regions around the world were very poorly developed in technical diving. Agencies intent on growth seemed to ignore that problem, choosing whoever was available, and regardless of their experience in the discipline, they would soon be teaching.
This decision to promote people with limited experience became especially problematic when it came to Instructor Trainers. People with almost no experience in something like trimix diving were qualifying trimix instructors. Watching this play out in agency after agency, and on continent after continent, was a troubling affair. Conversely, it took many years for GUE to develop and train people of appropriate experience, especially when looking to critical roles, including high-level tech and instructor trainers. At the same time, GUE’s efforts shaped the industry in no small fashion as agencies began to model their programs after GUE’s training protocols. Initially, having insisted that nobody would take something like Fundamentals, every agency followed suit in developing their own version of these programs, usually taught by divers that had followed GUE training.
This evolving trend wasn’t without complexity but was largely a positive outcome. Agencies soon focused on fundamental skills, incorporated some form of problem-resolution training, adhered to GUE bottle and gas switching protocols, reduced insistence on deep air, and started talking more about developing skilled divers, among other changes. This evolution was significant when compared to the days of arguing about why a person could not learn to use trimix until they were good while diving deep on air.
To be sure, a good share of these changes was more about maintaining business relevance than making substantive improvements. The changes themselves were often more style than substance, lacking objective performance standards and the appropriate retraining of instructors. Despite these weaknesses, they remain positive developments. Talking about something is an important first step and, in all cases, it makes room for strong instructors in any given agency to practice what is being preached. In fact, these evolving trends have allowed GUE to now push further in the effort to create skilled and experienced divers, enhancing our ability to run progressively more elaborate projects with increasingly more sophisticated outcomes.
The Future of GUE
The coming decades of GUE’s future appear very bright. Slow but steady growth has now placed the organization in a position to make wise investments, ensuring a vibrant and integrated approach. Meanwhile, evolving technology and a broad global base place GUE in a unique and formidable position. Key structural and personnel adjustments complement a growing range of virtual tools, enabling our diverse communities and representatives to collaborate and advance projects in a way that, prior to now, was not possible. Strong local communities can be easily connected with coordinated global missions; these activities include ever-more- sophisticated underwater initiatives as well as structural changes within the GUE ecosystem. One such forward-thinking project leverages AI-enabled, adaptive learning platforms to enhance both the quality and efficiency of GUE education. Most agencies, including GUE, have been using some form of online training for years, but GUE is taking big steps to reinvent the quality and efficiency of this form of training. This is not to replace, but rather to extend and augment inwater and in-person learning outcomes. Related tools further improve the fluidity, allowing GUE to seamlessly connect previously distant communities, enabling technology, training, and passion to notably expand our ability to realize our broad, global mission.
Meanwhile, GUE and its range of global communities are utilizing evolving technologies to significantly expand the quality and scope of their project initiatives. Comparing the impressive capability of current GUE communities with those of our early years shows a radical and important shift, allowing results equal or even well beyond those possible when compared even with well-funded commercial projects. Coupled with GUE training and procedural support, these ongoing augmentations place our communities at the forefront of underwater research and conservation. This situation will only expand and be further enriched with the use of evolving technology and closely linked communities. Recent and planned expansions to our training programs present a host of important tools that will continue being refined in the years to come. Efforts to expand and improve upon the support provided to GUE projects with technology, people, and resources are now coming online and will undoubtedly be an important part of our evolving future.
The coming decades will undoubtedly present challenges. But I have no doubt that together we will not only overcome those obstacles but we will continue to thrive. I believe that GUE’s trajectory remains overwhelmingly positive, for we are an organization that is continually evolving—driven by a spirit of adventure, encouraged by your heartwarming stories, and inspired by the satisfaction of overcoming complex problems. Twenty-five years ago, when I took the path less traveled, the vision I had for GUE was admittedly ambitious. The reality, however, has exceeded anything I could have imagined. I know that GUE will never reach a point when it is complete but that it will be an exciting lifelong journey, one that, for me, will define a life well lived. I look forward our mutual ongoing “Quest for Excellence.”
See Listings Below For Additional Resources On GUE And GUE Diving!
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.
A Few GUE Fundamentals
Similar to military, commercial and public safety divers, Global Underwater Explorers (GUE) is a standards-based diving community, with specific protocols, standard operating procedures (SOPs) and tools. Here are selected InDEPTH stories on some of the key aspects of GUE diving, including a four-part series on the history and development of GUE decompression procedures by founder and president Jarod Jablonski.
Anatomy of a Fundamentals Class
GUE Instructor Examiner Guy Shockey explains the thought and details that goes into GUE’s most popular course, Fundamentals, aka “Fundies,” which has been taken by numerous industry luminaries. Why all the fanfare? Shockey characterizes the magic as “simple things done precisely!
Back to Fundamentals: An Introduction to GUE’s Most Popular Diving Course
Instructor evaluator Rich Walker attempts to answer the question, “why is Fundamentals GUE’s most popular diving course?” Along the way, he clarifies some of the myths and misconceptions about GUE training. Hint: there is no Kool-Aid.
As you’d expect, Global Underwater Explorers (GUE) has a standardized approach to prepare your equipment for the dive, and its own pre-dive checklist: the GUE EDGE. Here explorer and filmmaker Dimitris Fifis preps you to take the plunge, GUE-style.
The Flexibility of Standard Operating Procedures
Instructor trainer Guy Shockey discusses the purpose, value, and yes, flexibility of standard operating procedures, or SOPs, in diving. Sound like an oxymoron? Shockey explains how SOPs can help offload some of our internal processing and situational awareness, so we can focus on the important part of the dive—having FUN!
Standard Gases: The Simplicity of Everyone Singing the Same Song
Like the military and commercial diving communities before them, Global Underwater Explorers (GUE) uses standardized breathing mixtures for various depth ranges and for decompression. Here British wrecker and instructor evaluator Rich Walker gets lyrical and presents the reasoning behind standard mixes and their advantages, compared with a “best mix” approach. Don’t worry, you won’t need your hymnal, though Walker may have you singing some blues.
Rules of Thumb: The Mysteries of Ratio Deco Revealed
Is it a secret algorithm developed by the WKPP to get you out of the water faster sans DCI, or an unsubstantiated decompression speculation promoted by Kool-Aid swilling quacks and charlatans? British tech instructor/instructor evaluator Rich Walker divulges the arcane mysteries behind GUE’s ratio decompression protocols in this first of a two part series.
The Thought Process Behind GUE’s CCR Configuration
Global Underwater Explorers is known for taking its own holistic approach to gear configuration. Here GUE board member and Instructor Trainer Richard Lundgren explains the reasoning behind its unique closed-circuit rebreather configuration. It’s all about the gas!
GUE and the Future of Open Circuit Tech Diving
Though they were late to the party, Global Underwater Explorers (GUE) is leaning forward on rebreathers, and members are following suit. So what’s to become of their open circuit-based TECH 2 course? InDepth’s Ashley Stewart has the deets.
Diving projects, or expeditions—think Bill Stone’s Wakulla Springs 1987 project, or the original explorations of the Woodville Karst Plain’s Project (WKPP)—helped give birth to technical diving, and today continue as an important focal point and organizing principle for communities like Global Underwater Explorers (GUE). The organization this year unveiled a new Project Diver program, intended to elevate “community-led project dives to an entirely new level of sophistication.” Here, authors Guy Shockey and Francesco Cameli discuss the power of projects and take us behind the scenes of the new program
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.
Tren Maya is on the Wrong Track! An Update.
Doping for Depth
Configure Me This: The Annotated Sidemounter
Hydrogen, At Last?
The Who’s Who of Sidemount
Hyperbaric Chambers Are Turning Away Divers. Will There Be One Nearby When You Need It?
The Aftermath Of Love: Don Shirley and Dave Shaw
Let There Be Mix!
