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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.

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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.

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).

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.

Additional Resources:

REPROGRAMMING THE FUTURE: AN INTERVIEW WITH KEVIN GURR

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

DELVING DEEPER INTO DEEP STOPS By Mark Powell


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.



Cave

An Underground Perspective on GUE’s Cave Curriculum

It’s difficult to objectively compare and contrast technical courses from different training agencies, and many agencies are less than enthused about the prospect. So when I learned that NSS-CDS cave instructor and training council member, Chris Brock had completed GUE’s cave curriculum, I was eager to get his perspective. On the record of course!

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by Michael Menduno

It’s difficult to objectively compare and contrast technical diving courses from different training agencies, and the agencies themselves rarely encourage the juxtaposition. Each has its own particular philosophical bent, focus, and of course, what the organization deems its secret sauce, which can be hard to quantify. As a result, thoughtful, informed perspectives are hard to come by, though they can be illuminating when you’re trying to grok the depth and breadth of our tech community’s education ecosystem.

Needless to say, I was excited to learn that my former cave instructor, National Speleological Society Cave Diving Section (NSS CDS) instructor Chris Brock, had taken GUE’s Cave 1 and Cave 2 courses—the equivalent to the CDS Cave Diver course with decompression procedures and its Stage Cave Diver course. Note that Brock is also a member of the CDS Training Council and an Instructor Sponsor. Accordingly, I reached out to him, hoping to query him on the record, of course, about his experience. 

The circumstances of the 52-year-old cave instructor’s participation in GUE classes were somewhat unique.  Brock had agreed to assist his friend and fellow cave diver Meredith “Mer” Tanguay, who was completing her GUE Cave 2 Instructor Exam with Instructor Examiner (IE) Daniel Riordan in late 2020, in the midst of the global pandemic. 

Tanguay presciently acted to “bulletproof” her IE class—Mer managing Mr. Murphy—by making sure she had qualified ‘students’ at hand in case there was a dropout. Brock had previously completed Cave 1 under Tanguay’s tutelage in preparation for that eventuality, so when she received a cancellation a week before Cave 2, he was ready to go. What a guy!

I should note that Tanguay, principal of Wet Rocks Diving,  is one of GUE’s ardent, hard working recreational, technical, and cave diving instructors, a Fundamentals Instructor Trainer (IT), and an IE for Rec 1 & 2. She has been diving with GUE for 18 years. She was the first female to successfully complete her GUE’s Cave 1 and Cave 2 instructor rating, and is currently the only one teaching both GUE Tech and Cave, and GUE’s only female Cave 2 instructor, which until now had long been the sole province of the boys. 

As luck would have it, I was able to connect with Brock, a former public school teacher who is also a TDI, IANTD and PADI tech and cave instructor, to ask him about his experience with the GUE cave curriculum. Here’s what the man had to say. 

Let me ask, if you had to pick one word or phrase to describe your experience taking Cave 1 & 2, what would it be?

Chris Brock: Procedural! Everything you do in GUE has a set procedure. For me, having been away from GUE for 10 years when I took my “Fundies” class, it was hard at first to be procedural when I have so much muscle memory from just doing the dives all these years without thinking about it. It was difficult for me. It was very procedural and I had to slow down. 

Danny had a memorable piece of advice for me. He said, “You just have to slow down because your mind is thinking so fast about it and the way you do it. You have to just take it step by step and slow back down.” So, my takeaway at this point is that it was ‘highly procedural.’

Ha! GUE IE Guy Shockey, describes the work of GUE courses is teaching divers “how to do simple things precisely.”  What did you like most about the courses?
Line drills. Photo courtesy of M. Tanguay.

What I liked most about the course was seeing different ways of teaching the same concepts that I teach. I found a lot of value in how GUE does gas switches. I plan to do that from now on and incorporate it into my teaching. 

Now, will I encourage my students to dive in a Hogarthian configuration? I don’t know that I can do that fully, but I think we can incorporate Hogarthian principles into every configuration, even if they choose to use a chest strap and things like that. I think there is simplicity there as well as some tips and tricks that I’ve picked up from Danny and Meredith that will be helpful to students. 

Danny also addressed some of the things that I’ve seen as a weakness to it, to the Hogarthian configuration. He showed me a lot of little tricks that I had not seen before that I will also incorporate. There’s a lot of stuff that I’m going to try to add into my courses as well.

What did you like least about the courses?

I told Meredith and Danny this too: I think the strategy of GUE from what I saw over the two weeks of class, is a whole lot of push, push, push, push procedure. And they push the intensity level so high that some divers don’t have time to assimilate it and let it sink in before the instructors push students further. 

I think you should push a diver only so far, let them relax for a little bit and understand what they’re doing, then push them again. And in that sense, I don’t think there’s enough time for assimilation because there was constant intensity on all 10 dives. There was a push on all of it. So that’s one thing I did not like. 

Anything else?
Chris Brock labeling his cylinders. Photo courtesy of C. Brock.

The second thing I did not like was that in some ways I found it too procedural to where they were stressing valves, stressing lights, stressing and breaking everything rather than teaching these people how to cave dive. [Ed. Note: GUE tech and cave classes focus heavily on scenario i.e. failure-based training.

Teach me proper technique in this type of tunnel, so that I can transfer that learning on how to do it in that tunnel over there. Or teach me proper technique for diving in flow, so I can transfer it to how to dive in a high flow tunnel, that sort of thing. 

There wasn’t enough of that modeling, in my opinion. There wasn’t enough of that kind of modeling from the instructor showing me how to cave dive. I mean the instructor would correct things. She would say, “Your frog kick needs work or has some weaknesses in it.” But sometimes, and I do this—I did it in your class—I’ll say, I want you to follow me and do what I do. I think instructors should do that. Those were the two things I mentioned in my debrief with Meredith and Danny. I told them that that’s not what I would choose to do.

Ah yes, I remember. You had me do that at the mud tunnel at Ginnie Springs, “Follow me and do exactly as I do.” I was going to ask you about that because it really struck me when I worked with you and Reggie [Former NSS-CDS training director Reggie Ross, who passed away in 2019] that your course focused on the cave, the cave environment, and dealing with the cave. 
GUE tech courses are typically scenario-based. I was curious about what your take was on that. I talked to Meredith and she told me that GUE’s focus is 50% on the cave and 50% on what one would call problem-solving. So, you’re saying that it seemed to you it was less on the cave and more on problem solving.

From my point of view, yes. They told us, “The first half of the dive is yours, the second half of the dive is ours,” and they offered some coaching, and modeled and tried to correct our technique. The problem with it was this: Everybody knows—or learns quickly by living through the first few dives—[that] it’s hard to relax during the first half of the course. In the first three and a half or four days of the six-day course, you’re not enjoying those dives. Because it’s all about breaking you down and stressing you out. 

I understand why Meredith says 50-50. Because they do coach on that 50% in. But there was never that time, and maybe it’s because I was there, that she didn’t have to do as much modeling. She could always put me in front, and there you have it. And she could stay out of the team by doing that. Yeah, that’s just my feeling on it; we did have a conversation about it. I think there should be more teaching cave diving techniques and not just breaking every valve under the sun.

Right. You mentioned that you thought there should be a bit more time for students to absorb the lessons between high stress periods. And you have a unique perspective because you are already a cave instructor. But let me ask, do you think that the focus on problem solving—that is, dealing with continual multiple failures—helps students build confidence and capacity? 

That’s a tough one to answer. The answer is yes and no. I think that managing these situations within the team and getting everyone out safely definitely ups the student’s capacity. Where I think it’s a no is that sometimes a set procedure of doing things is not necessarily the only or even—in my opinion—the best way of dealing with certain failures. But it does focus problems back on the team rather than on the individual and the prescribed procedure for dealing with them. 

I do find the whole thing very interesting and very challenging for those making the standards for GUE education. I mean writing procedures that can easily be utilized across all types of diving is a challenging undertaking.

You raised a topic I was going to ask you about, the team. Obviously GUE is known for its team focus versus focus on individual diver. Was that different? How did that come through in the class and how does that compare with CDS training? Did you find more focus on the team in this course than you would in a CDS class? 

Yes, there was much more emphasis on the team because in a CDS course we can teach a single diver and we put ourselves as the dive buddy with them. After going through this process I do believe having that second teammate is very important. Learning how to work together as a team is sometimes more difficult than learning to cave dive.

“After going through this process I do believe having that second teammate is very important. Learning how to work together as a team is sometimes more difficult than learning to cave dive.”



Ha! Like a lot of things, it’s a learned skill, or at least can be improved with training. 

Exactly! In the GUE course, you’ve got to have at least two student divers. Now, in both of these courses we were teams of three. It was interesting, on the first course (Cave 1) we had one guy that had a difficult time fitting in with the team. That’s not to say he was a bad person or anything like that. His personality was just different than the others and it was a difficult mix. The differences in how we looked at things did create some friction in the course as all of us had strong opinions. It was interesting.

In the second course (C2), I was paired with a husband and wife and they were fantastic. Just fantastic. I thoroughly enjoyed being teammates with them and we worked well together. Not to say there wasn’t friction on occasion, but never anything where you felt like the team was fragmenting. I enjoyed that piece of it quite a lot. 

Because you learned something?

I actually enjoyed it a lot because for me, it was a different way of thinking about stuff. I’m so used to doing most of these things on my own with one or two students. It forced me to be more conscientious of others around me and I had to make some changes in how I communicated. Having worked with Reggie, I am used to very direct communication. And I had to temper that on occasion with certain teammates because they did not respond well to that. So, I had to adapt. 

Brock tweaking his DPV with an onlooker. Photo courtesy of C. Brock.

That was helpful. Meredith would actually tell me, “Chris, you’re a little too direct; you’re being a little too direct underwater.” And I said, “Well Meredith, they’re doing X, Y, and Z.” And she said, “I know they are. I know they’re making mistakes. But you need to realize that these aren’t people that have done 1000 cave dives. You are raising their stress level with the way you are communicating.” 

So, I said, “You know what? You’re right. I need to work on this.” And so, I enjoyed that piece of it. In the CDS, we rarely teach teams of two and three, so it was good to participate in that.

I know that you did the classwork on Zoom beforehand and then got together for the diving. I have two questions here. First, I am guessing that with the pandemic still raging, more and more instructors from all agencies are conducting Zoom classes these days. How did you find that? 
Second, I’d be interested to get your take on the knowledge content, how it compared to a CDS or TDI cave course. Did you feel it was complete and well presented, that kind of thing?

I think Meredith does a fantastic job. She has gone to great lengths and spent countless hours putting her courses into an online learning environment. She has put a lot of time into lecturing online, presenting PowerPoints online, and providing supplemental resources online, and I found that very, very helpful. 

Tanguay conducted her cave class lectures and meet ups on Zoom.

We were running at eight in the morning until around seven at night, every night. And if you were to throw another hour and a half lecture on that, it would’ve been impossible. I have been using the TDI online course for my students, and I do like it. However, it is a supplement to my own lectures. The difference being that currently most of my presentations are done in person.

I worked through the TDI online full cave module a few years ago as part of my research for a story. It’s very different from a live lecture over Zoom. 

Yes, Meredith does active instruction because there is no packaged online course module for Cave One or Two. So, it’s active lectures and she answers questions and it was very helpful. I learned some things.  There are also some videos that I want to use, and I plan to incorporate GUE.tv in my own courses. So, I found it very helpful. I think the way that she is approaching online learning is the wave of the future and I think a lot more instructors should incorporate that into their teaching.

No doubt, things are going to remain crazy for a while, so this is a good impetus for instructors to think about online learning. I know many GUE instructors have gone that route.

Here’s what it does. As a student you get this very high level of instruction ahead of the course, and then you then have the opportunity to review that material as you’re getting closer to the course. You have an opportunity within the course to go dive and experience it, and there’s the opportunity to have much deeper conversations than you normally would because now you’ve experienced it three times before you ever really get into it. So, you’re already at a state of being able to formulate really relevant questions at the conceptual level versus just rote knowledge. 

I like what she’s doing with this. She’s raising the bar on getting the content across. It’s very good, it’s very good.

The class you took was Meredith’s Instructor Examination (IE) to become a Cave 2 instructor. I know you have participated in CDS Instructor Institutes. Talk to me from an IE perspective. How did the instructor examination come across? How did it compare to CDS’ instructor development process?

It was completely different. In the CDS, we can do our IEs in several different ways. Yes, if a candidate has a group of students, then we can just observe them teaching their students and that can be their IE. So, we can do that. But most of the time, candidates come to us. They do classroom presentations for us, they do land drills for us, they do in-water work for us. So we see all of that as instructor evaluators. 

In this case, Meredith had to take care of all of the details and she was being evaluated on everything: from logistics and pacing of the course, dealing with events that happened within the dive, the debrief, corrections that she would have to make in the dive regarding safety, or whatever. We had a couple of instances, two that I can think of. One student had had an ear problem on a dive and then we had a problem with a student that just wasn’t feeling it and he thumbed the dive early. Danny was of course evaluating everything.

It was completely comprehensive. I mean the whole thing was being looked at. That’s a lot different than what we do at the CDS. Meredith was really put through the ringer, without a doubt. 

All of my GUE instructor friends, most of whom have other agency certs as well, tell me that GUE sets a very high bar for their instructors: it’s hard to become one, they have to do a partial requalification annually, and a full requalification every four years.

They do. Meredith had to do her requalification too. She had to do the swims and climb stairs wearing her doubles. The whole enchilada.

So from an instructor’s perspective, how would you compare and contrast GUE’s overall approach versus the CDS’s?
Chris Brock stowing gear after a dive. Photo courtesy of C. Brock.

If you get a good instructor, a good, tough instructor in any agency, you can get a good cave class. But if you get a burned-out instructor, in any agency, you can get a bad cave class. 

What I saw was certainly the cream of GUE rising to the top. I saw Meredith’s best work; her preparedness was point-on because of what she was going through. And I’ve been around her in other situations where she’s teaching and she does set the bar at a very high level for cave instruction. I’m very impressed with her. Very impressed.

I would say GUE’s courses are well suited to people that are very motivated, high-level achievers who love that team camaraderie. And if that personality type is who you are, I think GUE is a fantastic route for you to go. If that’s not the kind of personality that you have, then you might struggle within it. 

“I would say GUE’s courses are well suited to people that are very motivated, high-level achievers who love that team camaraderie. And if that personality type is who you are, I think GUE is a fantastic route for you to go. If that’s not the kind of personality that you have, then you might struggle within it.”

So to say that it’s better than TDI, CDS, any of that, I can’t say that it’s better. Is it more intense? I would think, by and large, it is more intense. I do a lot of stressful stuff in my courses, but I don’t raise it to that level. I don’t know how I would’ve handled that if I hadn’t a lot of experience already. It wore on me over the days. 

In my experience, GUE courses tend to be fairly intense. Heck, GUE is fairly intense. Ha!

Yeah, they are. But here’s one thing, I will say this. One of the debrief questions at the end of the first course was this: Do you consider yourself a GUE diver? And I said, no, I’m not a GUE diver, I’m a cave diver. I’ll dive with anybody, anytime, who’s safe and looks out for their buddy. 

Now, at the end of the second course they didn’t ask that question so I told them, you should’ve asked me that question again. And Meredith said, “Okay, what would you say?” And I said, “I would’ve said, yes, I am.” Because there is something rewarding about being tested that hard, and receiving that credential. You earned it. You really earned that certification. 

“Because there is something rewarding about being tested that hard, and receiving that credential. You earned it. You really earned that certification.”

I don’t know that I am a GUE diver, but will I dive with GUE guys? Sure. Do I think there is some of the bullshit that hangs over from the old days? Absolutely. There is still some of that under the surface that I see, but by and large I have met a lot of really good people.

Chris Brock doing what he loves best. Photo courtesy of C. Brock.
I find your take on the type of diver who might find GUE appealing interesting. In my younger years, I was like, 150% pushing all-out, all of the time to improve my diving. And now, I find that mindset just doesn’t fit me quite as well. I’m more like, “Yeah, yeah, yeah, can we just go diving?” Maybe it’s just old age, I don’t know. I think it may actually be a bit healthier for me to not to push all the time. You know what I’m saying? I’m just a little more chill.

I’m the same way, and that’s kind of why I would challenge them. I don’t know if Meredith spoke to this. She could’ve had a much easier IE if I hadn’t been there. I was the guy that was challenging her on every point while she was getting evaluated on her responses to every challenge I made, by Danny. 

Ha! Right, some friend you are! Making it harder.

And Danny spoke about that in our debrief together. He said, “Chris, you brought a whole other perspective and Meredith had to defend what we do. That was good for her to have to defend it. Because you understand the various aspects of cave diving and are coming in and asking, “Why?” Tell me why because I’m not going to believe it on face value like a normal student who listens to the instructor say, “Do X, Y and Z,” and says, “OK,” instead of, “Why do you do it this way and not that?”

And I’m with you—I think that there is a personality type that fits GUE and there’s a personality type that doesn’t. And there’s a personality type somewhere in the middle that fits GUE sometimes but maybe not all the way. Perhaps that is me. Overall, I think it is a pretty solid program. I really do.

So you think there may be other GUE courses in your future? 

I do. I’m looking forward to my next professional development course with GUE. Either Tech 1 with Meredith or possibly a DPV course with Danny. As an instructor in both of those areas I am curious as to how that content is presented as well.

“I do. I’m looking forward to my next professional development course with GUE. Either Tech 1 with Meredith or possibly a DPV course with Danny. As an instructor in both of those areas I am curious as to how that content is presented as well.”

Thanks Chris! Thanks for being willing to share.

Footnote by Meredith:

Meredith Tanguay in her element. Photo by Annika Persson.

Appropriately challenging both “normal-track” Cave 2 students and a student with over 1000 cave dives in the same class most definitely added another layer of difficulty to my Cave 2 Instructor Exam class. It was certainly a challenge, and I like challenges, so I thank Team FIYD FIYD for that! [Ed.—Inside joke] Our job as instructors is to provide challenges to improve on each diver’s starting set of skills and help them become better and more efficient, even the ones that are already solid divers. This makes every GUE class different and customized for that unique team of students.

Additional Resources:

Meredith Tanguay, principal Wet Rocks Diving

Chris Brock, principal, Cavediving.com


Michael Menduno/M2 is InDepth’s editor-in-chief and an award-winning journalist and technologist who has written about diving and diving technology for more than 30 years. He coined the term “technical diving.” 

His magazine aquaCORPS: The Journal for Technical Diving (1990-1996), helped usher tech diving into mainstream sports diving and he produced the first tek.Conferences and Rebreather Forums 1.0 & 2.0. In addition to InDepth, Menduno serves as an editor/reporter for DAN Europe’s Alert Diver magazine, a contributing editor for X-Ray mag, and writes for DeeperBlue.com. He is on the board of the Historical Diving Society (USA), and a member of the Rebreather Training Council.

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