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Variable Gradient Model: An Approach To Create More Efficient Decompressions

British tech pioneer and inventor Kevin Gurr has been building dive computers since the early 1990s, including the world’s first mixed gas diving computer, the VR3, which he launched in 1997, through his former company VR Technology Ltd. based in Dorset, UK. He also designed and built three sport rebreathers. Now the Maritime Technology Officer at Avon Protection managing military rebreathers, Gurr discusses an innovative modification of gradient factors that he developed for use with his various devices.



by Kevin Gurr

Header Image: by K. Davidson for Halcyon.

This article is not designed to go into the finite detail of decompression modeling; other people have achieved this far more successfully. It is intended as a snapshot view of what is currently available in Avon Protections’ MCM100 military rebreather, which I helped design, hopefully with a level of technical clarity so that the reader can evaluate for themselves the merits of the differing methods.

The human body cannot currently be mathematically modelled. Not only are individuals different because of age, fitness, pulmonary and cardiac (PFO) defects, but they also vary on a daily basis due to hydration, stress, exercise, micro-nuclei generation, and many other factors. 

So how does the diving community conduct thousands of safe dives per year? Some experimentation has historically been done to produce ‘reasonably safe’ decompression tables that ‘fit’ most people for a shallow water (primarily air diving) environment. In modern technical diving, much of the deeper diving we do is simply an extrapolation of the early shallow water research. We now know that this does not always work. 

Shallow water diving is relatively well documented and we have historical figures to work with, which  is only just starting to occur with deeper diving. Let’s review the basic decompression theory so that we may investigate possible ways to deal with the problem.

Consider the Buhlmann system of decompression: it is assumed that each of the hypothetical tissue compartments can safely experience an over-pressurization during a reduction in pressure (ascent) after a pressurized exposure (time at depth) which has allowed them to absorb gas.

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The subsequent decompression profile that is generated on the ascent should not exceed the tolerated over-pressure value, or M value — a theoretical construct for the theoretical controlling tissue compartment within the body, in order to avoid decompression illness (DCI). As each compartment comes into play and the relevant M value is reached, a decompression stop profile is generated.

Figure 1 represents a very simplistic example involving just one of the fast tissues which will control the primary ascent phase. The M value for this compartment is shown as a straight line. If the diver controls the ascent, the inert gas loading in the compartment will stay on or below the M value line. If they do this, let’s assume they are using 100% of the available M value, which means there’s no extra safety margin for that dive; they are theoretically diving right on the edge of the model. 

Graph courtesy of Kevin Gurr.

For a typical bounce dive, Buhlmann standard practice has been to allow a rapid ascent to the first stop to generate a high level of off-gassing. Doing this, the gas loading in the fastest compartment will be on or near saturation at the bottom depth (the slow tissues are only partially saturated). This means that the fastest compartments will control the initial ascent since their gas loadings will be near or on the tolerated over-pressure value (M value). The first stop depth is set when the controlling (fast) compartment is nearest to the M value. The example only shows up to a point where the first stop starts and does not detail the other compartments or the remaining decompression. 

Using gradient factor terminology, the M value line is the 100/100 reference. The first 100 describes how close (in percentage) to the M value line the first stop is, and the second 100 describes how close the final stop is. Thus 100/100 has no added safety margin compared to the M value. In the complete picture, each compartments’ M value and each compartments’ internal pressure right through to the end of the dive (not just to the stop as drawn) would be displayed on the graph each with the same 100/100 gradient. The slower compartments would reach their M value during the final decompression phases while the faster compartments control the deeper decompression.

The gradient factor system modifies the M value by taking a percentage of the difference between the M value and the ambient pressure value. As a simple example to illustrate how Gradient factors work, using 80% of the M value as the controlling value (80/80 line) produces a line on the graph (figure 2) below the 100/100 line, having the effect of reducing the compartments allowed over-pressure value and generating a deeper decompression stop. 

Graph courtesy of Kevin Gurr.

Again, in the complete picture all the adjusted M values and compartment pressures would be plotted, adding safety to the whole decompression profile.

As most of these early dissolved gas based tables were formulated around relatively shallow water air range dives, they do not suit deep water dives, although historically they have often been extrapolated for use in deep-water. While these tables have a varying solution for different depths they were depth limited.

So what about Pyle stops? Technical diving pioneer, ichthyologist Richard Pyle developed a practical solution that divers could understand for modifying the decompression profile to reduce the excessive over-pressurization of the controlling compartment at the deep stops. He found that by stopping and venting a fish’s swim bladder below the first tabular stop depth, he ‘felt better’ at the end of the decompression. He was in effect allowing the faster compartments’ pressure to reduce before ascending to the tabular first stop and not reach its M value peak. 

The downside of this was that other compartments were still on-loading gas, which could generate an additional decompression obligation in shallow water. He was applying a safety factor that only had an effect on the deeper stops. This had the potential to allow the slower compartments to become closer to their M value during the shallow water decompression phase unless additional safety factors were applied.

Now we move onto bubble models (VPM etc.). Put very simply, bubble models attempt to explain the growth phases of inert gas bubbles and their subsequent effects. These models focus on the first part of the ascent where the bubbles grow, and by doing so, claim they can lead to a predicted reduction of the decompression obligation in shallow water. However, because of this decompression reduction, some dives generated decompression stress which could not be explained. In recent years, these bubble growth models have gone through several iterations as a result, and new evidence suggests that “deep stops” generated by bubble models may not be more efficient than shallower decompression.

A common (but complicated) solution to reduce the problem was to combine what was known about shallow water decompressions (Buhlmann) with the deep water bubble model. We know this is still an incomplete solution as phenomena such as arterial bubbles and other effects are not taken into account. Bubble models give an explanation and provide a working model of what Richard Pyle tried to implement practically from a technical divers standpoint. 

A recent tool, which provides a simpler solution between Buhlmann and the bubble models, has been to use gradient factors with a dissolved gas model which in turn modifies the M values of the controlling compartments (Baker). This has the effect of combining a bubble with a dissolved gas model style decompression profile.

Gradient factors can further mimic bubble models by using two different gradient factors to control the decompression: one that primarily references the deep stops, and one the shallow. 

So a 20/80 gradient factor, which has been commonly used on deeper dives, would allow an over-pressure value of 20% (instead of 100%) of the difference between the ambient pressure and the allowed M value for the controlling compartment of the first or “deep stop” and 80% (instead of 100%) of the M value for the controlling compartments’ pressure difference at the shallow stop. The stops in between are calculated by drawing an over-pressure value line between the two points and plotting the new adjusted M values for each compartment in between. It assumes a linear calculation between the adjusted first and last M values. 

In Figure 3 let’s assume that compartment 4 controls the deep stop and compartment 16 the shallow stop. Again, for clarity, the on-going compartment inert gas loading reductions are not shown past the M value point, neither are all the other compartment M values.

Graph courtesy of Kevin Gurr.

The major drawback of gradient factors is that the factors applied need to be adjusted for each depth/time exposure. For example, if you used the same 20/80 gradient factor for an 80 m dive, on a 30 m dive you might have an excess of decompression in shallow water because we know from experience that a gradient factor of close to 100/100 is reliable for this shallow water dive. 

What does this mean? First, it is not necessarily appropriate to apply one gradient factor to a range of dive depths. What works deep may not work shallow. Secondly, it means just applying gradient factors in the first place may be too coarse a solution. Just drawing a straight line between the M value points and assuming the mid-water decompression follows this linear approach may not work. So how do we generate a refinement?

Stochastic modelling has been around in diving for some time. Decompression tables are generated based on statistical dive data of incidents; basically, points are plotted on a graph and an algorithm generated. So how could we use this to improve gradient factor modelling? Assuming the 100/100 factor is OK for a certain shallow dive and the 20/80 is OK for a particular deep dive, would it not be best to have a varying gradient factor depending on depth/time exposure and other factors? If we can be fairly certain of key decompression times for a range of depth/time exposures that are ‘safe’ and generate reasonable decompressions, we could use them to generate a gradient factor that varies accordingly. My term for this approach is a Variable Gradient Model (VGM).

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VGM has the ability to use stochastic data and historically ‘proven’ decompression values in an algorithm and automatically adjust it for a range of depth/time exposure scenarios. The VGM software can be embedded into the dive computer, for example, in the MCM100, and its parameters can be adjusted using the screen below. Note that I also used VGM in my previous company’s [VR Technology Ltd.] VRx computers.

The Ace, Ace Profile, VR3, VRx dive computers designed and built by Kevin Gurr, VR Technology Ltd.

In summary, a VGM profile has the effect of padding the stops at certain decompression points while reducing stop times at others for a specific exposure scenario. What’s more, it changes them again automatically for different exposure scenarios and allows varying degrees of user input dependent on the application. VGM is a useful tool based on our current culminated experience. It brings together in one approach much of what we know and may help predict some of that which we do not.

Once data is available, many other variables could be built into a VGM matrix, such that with time and information it could continuously evolve to give increasingly accurate decompression predictions. While the modelling of the human body eludes us, VGM would appear to be a good solution to the current issues.

Dive Deeper:

InDepth:  Gradient Factors in a Post-Deep Stops World by David Doolette.



Kevin Gurr has been involved with Technical Diving since its inception in Europe. As well as being the first Technical Diving instructor outside the USA, he has led and been a part of many expeditions; the first sport dives on the Britannic in 1997, treasure hunting in the Pacific (and several other locations World-wide), filmmaking, and a dive on the Titanic in the MIR submarines to name a few.

As an engineer and diver he has developed several ground breaking products for the diving industry from trimix computers to rebreathers, including the Ace Profile, VR3, VRx computers, Pro Planner desktop decompression software, and the Ouroboros, Sentinel, Explorer and the MCM100 rebreathers. He lives in Dorset, England with wife Mandy, daughters Leyla and Amberlee, Neo the black Labrador, and various motorcycles.


The Way The World Will Learn to Tec: Exploring PADI’s TecRec Update




By Michael Menduno. The views and opinions expressed are strictly my own. Photos courtesy of PADI unless noted.

This October at the annual Diving Equipment & Marketing Association (DEMA) tradeshow, PADI released a long-awaited update to its open circuit “TecRec” program, which was originally launched in 2001. Specifically, the training juggernaut has completely rewritten its introductory courses to tech diving, i.e., its Tec 40, 45, and 50 courses that serve as the gateway between recreational and technical diving. 

The update incorporates the latest diving science and thinking on topics such as gas density, gradient factors and deep stops, the helium penalty, whether oxygen is narcotic, dive planning software, and more. It enables divers to do their training in sidemount or backmount, adds additional “dry” practice session options into courses, and now offers trimix as a gas option beginning at 40 m/130 ft—originally the program was air and nitrox only. 

In addition, PADI added a Discover Tec (try-dive) and Tec Basics (skills) courses as additional resources for would-be tekkies and instructors. PADI’s advanced trimix courses, Tec 65 and Tec Trimix (which are newer) and its closed circuit rebreather (CCR) program (which was launched in 2012) remain largely unchanged. The updated TecRec courses are available now, though the original courses can be taught until 2025. 

“We think it’s the most robust and comprehensive program on the market,” PADI’s Michael Richardson, a Supervisor for Instructor Development, boldly asserted to me at the show. His comment got my attention, and I was interested to know more.

The TecRec update signals a conscious move on PADI’s part to lean forward into Tec diving and make it more accessible to interested recreational divers, while providing increased flexibility and resources for instructors and dive centers to expand their technical diving business. As discussed in PADI’s member materials, though tech divers only represent about 7% of recreational or sport divers, they are not only more engaged but spend considerably more money on equipment and training—as we know!—making them a lucrative market niche. “Tech diving is the future of the market,” opined Asutay Akbayir, PADI Regional Manager for the South Mediterranean, who has been involved in the TecRec program since its inception.

In fairness, though PADI is not regarded as tech brand, its sheer size and market presence with 128,000 members (instructors and dive masters), 6,600 dive centers in 184 countries, and (according to PADI) an estimated 70% of the open water market—The Way the World Learns to Dive—makes them an important player in the tech market. 

Though they declined to answer me specifically, PADI likely has upwards of 4-5,000+ Tec and rebreather instructors at various levels (personal communications)—second only to Technical Diving International (TDI)—and sports at least 366 designated TecRec centers in 64 countries, though many more dive centers offer tech training. And though they also declined to answer my questions on certifications, PADI is probably responsible for having brought tens of thousands of new tekkies, well, in this case, “Teccies,” into the fold. 

By focusing on the transition from Rec to Tec—arguably an area of strength for PADI which dominates the recreational market—the training giant will not only help create more tech divers but likely stands to grow the market—The Way Many Will learn to Tec? —and in doing so gain market share. They will also likely gain Tec instructors. According to PADI, 55% of all technical diving instructors globally are also PADI professionals, which means that the organization has direct links to those that can potentially help grow its tech training business.

PADI’s prospects for picking up new business are arguably further enhanced by the high quality of PADI’s new Tec eLearning materials and standards which seem to combine the best of old-school tech with the latest developments. Though some tekkies seem to enjoy PADI bashing—ironically both PADI and Global Underwater Explorers (GUE), which hosts InDEPTH, seem to be favorite targets for critics, though for different reasons—most tech professionals will likely be impressed by PADI’s latest efforts, which were more than two years in the making. I know I was. 

Accordingly, here is a brief review of the history of PADI’s TecRec program and a discussion about some of the details of the new update.

Photo courtesy of Ricardo Castillo for Dive Rite

A Dive into Tec History

PADI’s Diving Science and Technology (DSAT) division released its Tec Deep Diver program in 2001. The general approach at the time was to treat technical diving like cave diving, in that it shouldn’t be promoted, but if people were interested, the training was available. Note that DSAT, which served as PADI’s tech division for a time, was also a sponsor of Rebreather Forum 2, held in Redondo Beach, CA in 1996, and published the Proceedings.

Tec Deep Diver was an extensive course, typically taught over an extended time, with numerous days and or weeks devoted to training. It included 12 air or nitrox dives to a max depth of 50 m/165 ft, and a dense 378-page manual. By comparison, an Intro to Cave followed by Full Cave course today, would generally run 8-10 days and include 16 dives. In about 2009, the Deep Diver course was broken up into three modules: Tec 40, Tec 45, and Tec 50, indicating maximum course depth in meters, but the content remained largely unchanged. 

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Instructors I asked told me that the Deep Diver course was challenging to teach. First, the time requirements meant it was very difficult to fit into student and instructor schedules. Breaking the course into modules helped some, but the sheer volume of content was daunting. The course was developed when mixed gas dive computers and dive planning software were still in their infancy, so students were left to deal with extensive math calculations with a pen and calculator.

The original course was also conducted solely on air or nitrox blend. In fairness, back in the day, the community, by and large, limited air diving to 57 m/187 ft, based on a PO2=1.4 bar, and considered narcotic levels manageable at those depths. It was only later, pioneered primarily by GUE, that the recommendation to maintain Equivalent Narcotic Depths (END) at 30 m/100 ft by adding helium to the mix. 

As a result of the further work on gas density, Dr. Simon Mitchell and Gavin Anthony, concluded that air diving be limited to less than 40 m (gas density less than 6.3 g/l). To be sure, PADI received internal and external feedback and scrutiny over the last few years  regarding their approach to what is now considered “deep air” diving, and deep air diving with students. They were not alone. Their new recommended trimix options address this.

Finally, the original course material became seriously out-of-date with regard to important new developments in diving science and safety, including gas density as mentioned, gradient factors and deep stops, narcosis levels, the helium penalty, whether oxygen is narcotic, Immersion Pulmonary Edema (IPE), using dive gauges and tables versus dive computers, the use of dive planning software, and more.

Course Structure and Logistics

As far as the requirements for the courses, Tec 40 requires a PADI Advanced Open Water and Enriched Air Diver certification (Rescue Diver is recommended), the Deep Diver certificate or at least 10 dives to 30 m/100 ft, and at least 30 logged dives. The student must be at least 18. Tec 45 requires Tec 40, an additional Rescue Diver certification, and a minimum of 50 dives (≥10 dives to at least 30 m/100 ft). Tec 50 requires Tec 45, and a minimum of 100 dives or 75 hours. No doubt, a discussion could be had on how much experience someone should have before starting on their tech journey.

Course specifications are as follows: Tec 40 can be conducted on a single tank provided it has a Y-valve for redundancy, or backmount or sidemount doubles, depending on the students’ certifications, along with up to one deco gas with a maximum of 50% oxygen. The course includes four dives to α max depth of 40 m/130 ft with a maximum of 10 minutes of decompression on back gas, or 15 minutes using deco gas. The course has a trimix option with a minimum of 21% O2 and a maximum of 35% helium.  

Tec 45 is conducted in doubles back or side mounted cylinders and one deco gas up to 50% O2, with four dives to a maximum depth of 45 m/148 ft and a trimix option. There are no decompression time limitations. Tec 50 also consists of four dives to a maximum depth of 50 m/165 ft with double cylinders, two deco gases, one of which can contain up to 100% O2, and (optionally) normoxic trimix, with no more than 40% helium. Again, there are no specified deco time limits. 

The courses, which are performance based, intentionally have a lot of flexibility in scheduling using eLearning or class presentations (depending on language), however a typical schedule might be 3-4 days for each course, depending on the needs of the students. The instructor may also begin with the Tec Basics module to bring up divers’ skills prior to beginning the Tec 40-50 sequence.

Courses include an “Instructor Wetbook” for each class that instructors can take in the water as part of their tool kit. The Wetbook essentially outlines the conduct of the course and includes performance goals, checklists, skills to be learned, specifications for conducting each dive, etc. It is the only physical learning material used in the courses.

Taken as a whole, the Tec 40, 45, and 50 courses represent a comprehensive introduction to technical diving consisting typically of 9-12 days of training and 12 dives. To put this into perspective, by comparison earning a “tech pass” in a GUE Fundamentals class followed by a GUE Tech 1 course (dives to a max 50 m/165 ft  depth with trimix 21/35, one deco gas (up to 100% O2) and a maximum of 30 minutes of deco), typically would require 10 days of training and 13 dives. So, the two are roughly equivalent in terms of training time and number of dives.   

Photo courtesy of Jon Milnes

My Impressions

I decided the best way to assess the new courses was to dive in and work through the eLearning modules. It should be noted that PADI pioneered the use of eLearning in diving, back when digital meant floppy discs. Remember them?

I was impressed that the authors were able to seamlessly weave together old school tech philosophy and approach with the latest diving science with a focus on diver safety. Overall, it was some of the best tech course material I’ve read.

Tec 40 begins with a sobering warning. 

To sum up the difference between recreational and technical diving risk in a single statement: “In technical diving, even if you do everything right, there is still a higher inherent potential for an accident leading to permanent injury and death. You have to accept this risk if you venture into technical diving. “

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The warning is straight out of the original tech playbook pioneered by Capt. Billy Deans, before there were formal tech certification classes. Back in the late 1980s/early 1990s, interested divers traveled to Key West to spend a week, 10 days, two weeks—as much time as they could spare—to learn mixed gas diving from Capt. Billy. This was before formal tech certification courses existed.

By way of background, Deans’ best friend John Ormsby died on a deep air dive on the Andrea Doria in 1985. Deans was one of the divers that recovered the body and brought it back to the RV Wahoo. The incident motivated Deans, who worked with Dr. Bill Hamilton, to swear off “deep air diving” and develop his mixed gas diving operation and offer training.

On the opening day of his classes, Deans would welcome everyone. “We’re here to have a good time, “ he would say. “But before we do, I need to have your attention.” He would then play the film of him and others recovering his friend’s lifeless body and hoisting it onto the back deck of the Wahoo. “As I said, we’re here to have fun, but this is serious. You have to pay attention, and do everything right—there’s no room for complacency. If you don’t, you’re going to die.” Deans was admittedly harsh by today’s standards, but his admonition never failed to get divers’ attention. 

It was encouraging to see attitudinal requirements and discussions as an integral part of the course. Attitude requirements were of course, part of original “Blueprint for Survival 2.0” community consensus of best tech diving practices that was published in aquaCORPS Journal #6 COMPUTING (June 1993), and meant to help improve tech diving safety. 

To quote the Tec 40 text, “Your actions, words, and behavior must reflect that you will choose to follow the procedures, rules, and principles you learn in this course. This attitude is considered particularly important to diver safety in technical diving.” 

In fact, Tec 40 offers six characteristics that denote a responsible technical diver, to wit; self-sufficiency, team player, disciplined, wary, physically fit, accepts responsibility. Sounds about right to me. 

Finally, in the wrap up, the Tec 40 text reminds would-be tekkies (paraphrasing), “Your primary mission in tech diving is to survive the dive!”


It’s The Science, Stupid

As mentioned above, the Tec course materials integrate the latest science and thinking from gradient factors and gas tolerance to IPE and offer depthful and nuanced discussion. The latest science, for example, has concluded that oxygen is non-narcotic in the PO2 relevant ranges for tech diving, however, the discussion points out that there’s nothing wrong with adding extra conservativeness and treating both O2 and N2 as narcotic gasses in calculating one’s END. 

Similarly, the material teases out the nuances of the so-called “helium penalty,” a feature of some decompression algorithms that add extra deco time when using helium, whether or not it’s physiologically needed, and what that means for tech divers. They have also eliminated “deep stops,” which were included in the original Deep Diver course and offer an explanation why. 

I was also impressed with the level of detail. For example, in discussing gear configuration, the text points out that tekkies don’t use hose protectors because they can mask hose damage. Similarly, in discussing the use of hyperbaric mixes, it details the risks of oxygen fires, the need for proper cleaning and lubrication, and even highlights the fact that regulators made with titanium might not be fully compatible with oxygen use (check with the manufacturer).

As mentioned, the mathematics and calculations sections focus on using dive computers and dive planning software to arrive at the answers rather than doing manual calculations. Hmm, it’s faster and more accurate. PADI calls it a “real world” consideration. Geeks like me can follow the link to the formula details and calculations, if that’s what they need to learn the material. 

Drills & Skills

The Instructor Wetbooks outline the drills and skills to be worked during both dry and in-water sessions. I found them to be quite comprehensive and included the drills and skills you’d expect; dive planning, pre-dive checklist and equipment matching, S-drill, bubble check, controlled descent, propulsion drills, valve drills in trim, putting on and removing stage bottles, regular SPG checks, gas sharing, SMB deployment and ascent practice, proper gas switching, calculating SAC rates, etc.

As they work their way through the courses, students spend increasing time on problem-solving and responding to team emergencies such as free flows and leaky valves; various out of gas scenarios (bottom gas, deco gas); dealing with a dive buddy breathing the wrong gas at depth; buoyancy device failures; dive computer failures; and rescuing an unconscious diver. GUE Tech students will be very familiar with these kinds of drills.   

Recommendations & Standards

I found the recommendations and standards presented in the courses robust and reassuring, and if offering a recommendation vs. making it a requirement is insufficient to satisfy a dyed-in-the-wool, old-school GUE instructor, it would likely at least get her to at least give a nod of support. One of the considerations for PADI, with its ginormous, global scale, is that courses must have sufficient flexibility to meet the needs of divers and instructors in different geographies. Here are some of the high points.

PADI recommends that tech divers maintain an END ≤30 m/100 ft and gas density less than 6.3 g/l (the air equivalent of 38 m/128 ft); however, it does not mandate the use of trimix for the Tec 40-50 courses. Given current prices and availability issues with helium, it is recommended but optional in these ranges, depending, of course, on conditions and the circumstances.

PADI focuses on team diving. They also recommend that the team utilize the same gas mixes while conducting a dive—hard to argue against for obvious reasons—although PADI does not offer specific standard gas mixes like GUE (nor do other agencies). However, they do rely on standard gas switching protocols, in PADI parlance, the NO TOX gas switch (Note your tank label, Observe your depth, Turn on the valve, Orient the regulator hose, eXamine your teammates). 

Divers are encouraged to always use checklists. Gas reserves are calculated using traditional thirds or “Rock Bottom” gas, the equivalent to GUE’s “minimum gas” i.e., the amount of gas required to get two divers back to usable gas, whether deco bottles or the surface. Divers are also able to use computers in gauge mode and tables or dive computers. 

Photo by Imad Farhat, courtesy of Halcyon Dive Systems

In Conclusion

Overall, I came away very impressed with the program and its focus on diver safety. But I wanted to get a perspective from someone who was familiar with PADI Tec as well as other agency programs. In this pursuit, I had the privilege of speaking with  underground veteran Jim Wyatt, principal of Cave Dive Florida.

The ex-Navy diver is a former training director and instructor trainer for the National Speleological Society-Cave Diving Section (NSS-CDS) and a trimix instructor and cave instructor trainer for both IANTD and TDI. As far as his involvement with PADI, Wyatt is both a PADI course director and DSAT instructor trainer who has taught PADI Tec since 2002. Just the guy I wanted to talk with. “PADI Tec is a good program. They’ve made big changes and added trimix to their intro classes. I’d put their standards against anyone’s,” Wyatt, who’s hardly unbiased but likely knows the material as well or better than anyone outside the PADI organization, explained to me. 

It is important to remember that all training agencies have standards; the critical question is, do their instructors follow them? After all, it is the instructors who are entrusted to provide training to students. 

Without doubt, this is the work and challenge shared by all agencies, especially in the realm of technical diving. The challenge is even more complex for larger agencies like PADI and TDI, who have thousands of technical instructors. Managing and ensuring adherence to standards and quality instruction is undoubtedly a formiable task, even for smaller agencies like GUE, who have several hundred instructors.

Clearly, PADI bears the responsibility of ensuring that the quality of their Tec instruction matches the high quality of their standards and learning materials. I have no doubt that’s PADI’s goal and intent, and we wish them the utmost success in that endeavor. 

Growing our cherished community with well-prepared, competent and capable technical divers, especially among the next generation who will eventually take the helm, is a shared responsibility, irregardless of the logo. With a shout out to GUE, we need to encourage and inspire each another, and our respective organizations, to strive for excellence in this regard! It’s all of “OUR” global community after all.

Special thanks to Asutay Akbayir, Eric Albinsson, Vikki Batten, Chris Brock, Samantha Pearson, Michael Richardson and Karl Shreeves for their help with my research for this story.


aquaCORPS archives: Put Another Diver In: John Cronin And The Business Of Marketing The Diving World (OCT 1995) I interviewed the late PADI CEO John Cronin in his office in 1995 just as the training juggernaut was rolling out its new Enriched Air Nitrox program. We talked about the founding of PADI, his vision of the diving business, the impact of tech diving on the market, PADI’s new enriched air nitrox courses,  his thoughts on tech training and rebreathers, and where he believed the market was headed. Here is the original interview as seen in aquaCORPS.  It ran as the cover story of aquaCORPS #12 Survivors OCT 1995.

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

Alert Rapture of the Tech: Depth, Narcosis and Training Agencies 

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

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