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Off the Deep End? What You Should Know About Pool Chemistry

Now that pools are re-opening for swimming and training, we thought it fitting for us to take a bit of a deep dive into pool chemistry. Fortunately, Reilly Fogarty’s got the scoop on what’s going on in your favorite pool.

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By Reilly Fogarty
Header image by GUE instructor Steve Millington, http://socalscubadiving.com.

When divers dream of adventure, it’s not often that their mind wanders to images of the shallow end of the local YMCA pool. Adventures may not often take place in waist-deep water, but a chlorinated escape from our terrestrial confines can do a great deal for our health and safety. Between fitness, training, and cooling off on a hot summer day, you’ll spend a lot of your life in a pool, so you should know what you’re swimming in. Here’s the scoop on what’s going on in your favorite pool.

Swimming in History

Pools have been used for recreation, religion, and fitness for longer than history has been recorded. The first man-made swimming pool is thought to be the Great Bath of Mohenjo-Daro, a thirty-by-twenty-three foot bath created sometime in the 3rd century BCE. This structure was predated by a pair of religious pools located in Sri Lanka built nearly a century before. The first heated pool is credited to Gaius Maecenas, who may have been the architect of a bath heated by fire pits in Rome around the first century BCE. It’s not hard to see why ancient societies wanted the pools—from religious ceremonies to block parties, the uses for pools haven’t changed dramatically over the centuries.

Pools have been around for more than 2000 years. Photo by Saqib Qayyum / CC BY-SA (https://creativecommons.org/licenses/by-sa/3.0)

From these earliest pools sprouted dozens of similar structures across the globe. The logistics of building and maintaining the pools limited their use to only the most affluent until their popularity exploded during the mid-19th century with the rapid advent of new building technologies. Six indoor pools were built in London in 1837, and then the creation of the modern Olympic Games in 1896 rapidly spread public demand for public pools. 

Leaps in technology in the 20th century brought chlorination and filtration systems to pool design, and made pools easier to both build and maintain. The brick and tar construction of early history gave way to a flexible alternative, gunite, and soon after above-ground pool kits hit the market. Once the cost to build a pool dropped to levels attainable by common folk, they came to American backyards in droves. How to keep all those pools clean, however, was another issue. 

Pathogens & Pool Noodles

Once upon a time, the only way to clean a pool was to drain it and refill it regularly. Pools were often built on downward slopes to help drain them, and the water was cycled frequently. In the late 19th century people began to worry about large bodies of freshwater becoming disease ridden.

The first attempt to sterilize a pool in the U.S. using chlorine was at Brown University in 1910. The 75,000-gallon/284 kiloliters Colgate Hoyt Pool was chlorinated by graduate student John Wymond Miller Bunker, who used a bleaching powder, hypochlorite of lime (calcium hypochlorite), which had been recently discovered as a method to treat drinking water, at a concentration of 0.5 ppm. The pool remained sterile for four days. Bleaching powder, including both calcium hypochlorite and sodium hypochlorite (both a form of chlorine) instantly became the standard in pool sanitation, and spread across the world. 

Laws dictating pool sanitation appeared, and soon after diatomaceous earth filters hit the market. The filters use powdered rock to capture particles in the water and are frequently combined with skimmers, devices that filter larger objects from the surface of the pool through a mechanism similar to a storm drain. Pool use continued to increase in popularity and owners dabbled in a number of purification systems, from ultraviolet light, to ozone gas, to the chlorine and salt chlorinator systems most pools use today. 

Chlorine can cause irritation of the eyes and airways. Photo by Ted Harty, www.freedivingsafety.com 

Purification systems aren’t without their flaws. Put too much chlorine in a pool and you risk irritating your eyes and airway, causing rashes, breathing difficulties or even chemically burning the fine hairs off your body. More commonly, the combination of chlorine with the ammonia found in urine can create compounds called chloramines, or cyanogen chlorides. Chloramines cause the typical “over-chlorinated pool smell” we associate with hotel pools, and can cause skin and eye irritation, as well as exacerbate allergies or asthma. Cyanogen chloride can interfere with the body’s ability to use oxygen and can be fatal—thankfully it’s volatile and rarely forms in dangerous concentrations and degrades quickly when it does. 

Pee isn’t the biggest concern for pool hygiene, despite the fact that swimmers leave, on average, about a shot glass worth of urine every time they jump in.

Pee isn’t the biggest concern for pool hygiene, despite the fact that swimmers leave, on average, about a shot glass worth of urine every time they jump in. [Ed.note: Fitness and competitive swimmers urinate in the pool!] We tolerate the hazard and complications of chlorination because of the microbial risks associated with large numbers of people effectively bathing together. The World Health organization (WHO) points to Shigella and Escherichia coli O157 as bacteria of particular concern for swimmers. 

Competitive swimmers urinate in pools. Photo from Abbie Fish, swimlikeafish.org

Bacterial outbreaks are relatively rare among pool use but these bacteria, as well as a host of viruses, protozoa and fungi can be passed from swimmer to swimmer with relative ease. Both bacteria cause vomiting fever and diarrhea, although E. Coli O157 can cause hemorrhagic colitis and haemolytic uraemic syndrome (HUS) in severe cases. Giardia and Cryptosporidium are two protozoa that also pose a risk to swimmers, both being carried with fecal material. Both are highly resistant to disinfectants, are very infectious, and are shed in high densities by those infected. Diarrhea, cramping, vomiting and fever are common symptoms of both. Adenovirus, hepatitis A, norovirus and echovirus round out the list of common contagions in pool water, each with their own unique symptoms. 

There are a number of less common viruses and bacteria that can pose a risk to swimmers, but it’s worth noting that very few instances of group infection can be traced back to pool water. For the most part, modern pools are quite safe, and a combination of sterilization (to kill pathogens) and filtration (to control fecal release and other contaminants) can effectively keep a pool safe. 

The Mystery of Chlorine

Interestingly, the mechanism of chlorine sterilization is not fully understood. Research from the mid-20th century seemed to show that chlorine would react with some biomolecules as a result of it’s division into hypochlorite and hypochlorous acid in water. Later work indicated that chlorine likely reacted with a variety of bacterial targets and specific nucleic enzymes and membrane lipids – this was called the “multiple hit” theory, as explained in this 1998 Scientific American article titled, “How does chlorine added to drinking water kill bacteria and other harmful organisms? Why doesn’t it harm us?

Chlorine can eliminate a wide range of contamination factors. Photo by kappykeepers.com

More recent work suggests that chlorine specifically attacks cell walls by altering them physically and chemically, killing microorganisms by interrupting cell functions. Mechanically this theory involves a few steps. First chlorine disrupts the structure of the cell wall. This allows components of the cell that are critical to its function to escape, which causes a chain reaction of function termination, and eventually cell termination.

What this means effectively is that chlorine can kill a wide range of pathogens in relatively low doses. The concentrations used in public pools and water supplies are carefully monitored and designed to be small enough that ingestion of a normal amount allows only enough chlorine into the intestinal tract as can be neutralized by the action of the digestive system. That’s not to say that chlorine isn’t toxic – it can be extremely dangerous and must be handled with care – but like many poisons the dose determines the lethality. Because the concentrations used in pools are so low, the amounts that humans are likely to ingest are not harmful. 

At low concentrations chlorine in the body can be neutralized by harmlessly reacting with food in our stomachs, material in our intestinal tracts, or by the acidic environment of the stomach.

At low concentrations chlorine in the body can be neutralized by harmlessly reacting with food in our stomachs, material in our intestinal tracts, or by the acidic environment of the stomach. The Environmental Protection Agency (EPA) works closely with water utilities and environmental groups to reassess safe chlorine levels in drinking water and pools on an regular basis, and these guidelines along with those from the CDC should be used to determine what chlorine concentrations are safe for normal use.



Bug Count

The Centers for Disease Control  do provide some recommendations for specific chlorine and levels for pool use. Free chlorine in a concentration of a minimum of 1 part per million (ppm) in a pool, or 3 ppm in a hot tub, and a pH of 7.2-7.8 provides a safe concentration for swimmers and should kill most bacteria within a few minutes. Because bacteria levels are so difficult to measure in real time, testing is expensive, and equipment is scarce, regulations focus on mandating minimum free chlorine levels that are based on the environment rather than changing sanitation regulations that are based on bacterial load. This works on the assumption that known chlorine concentrations will kill common bacteria in a reasonably effective manner, and free chlorine indicates a sanitized body of water with a margin of safety. 

Something that might be confusing is the common chlorine smell found around high-traffic pools. This is actually caused by chloramines, the byproduct of a reaction of chlorine and urine, and can give off a strong odor and irritate the eyes, skin and airway. While the smell would seem to indicate that there is too much chlorine in the water, the opposite is actually true—eliminating the smell requires the superchlorination of the pool. Superchlorination, or “shocking” oxidizes the chloramines and leaves only free chlorine by flooding the body of water with chlorine levels five to ten times the normal concentration. Bathing during superchlorination is ill-advised, but the process should be done once a month in most cases, or once a week in hot weather. 

The risk posed by fecal contamination is much greater than general bacterial shedding, and diarrheal contamination is significantly higher-risk than a formed fecal incident. Both types of contamination require a fairly rapid response to minimize infection risk, effectively removing swimmers, isolating the hazardous material and superchlorinating the pool to disinfect it. The primary concerns with fecal contamination are Giardia and Cryptosporidium. While Giardia can be eliminated in as little as 20 minutes through superchlorination, Cryptosporidium is chlorine-resistant and can take as long as 25.5 hours to be safely removed. 

Treating Pools

Methods to treat pools have changed over the centuries, but only chlorine and a few similar chemicals have proven really effective. From alternatives like ultraviolet purification, to ozone, to constantly moving water, chlorine alternatives have failed for centuries and left us with traditional chlorine, bromine, and cyanuric acid. 

Chlorine used as free chlorine is fairly straightforward to use—it’s added to the pool and kills microbes. The disinfectant can be added as a liquid, tablet, stick, or granular powder. These products are typically a sodium, lithium or calcium base bonded to chlorine to stabilize the product and prevent dangerous accidental exposures. When dissolved in water the bonds between the chlorine and it’s stabilizing compound break and the free chlorine is released. This free chlorine is actually not the compound that disinfects the pool, but it must be broken down one more step to hypochlorous acid through dissolution in water. We can estimate hypochlorous acid concentration fairly accurately through the known reaction with water, so it’s easier to deal with these chemicals as “chlorine” in broad terms. 

There is a bit of an art to keeping chlorine levels in check, as too little chlorine will allow bacteria to grow and too much will cause skin and mucous membrane irritation, but chlorine sanitization is more labor than rocket science. The average public pool should have somewhere between 3 and 5 parts per million of free chlorine, while jacuzzis may require up to 10 parts per million, due to the hot environment providing an incubator for bacteria. 

Salt water pools are now common as well, but these too rely on chlorine. In a salt water pool a salt cell or generator breaks down the components of salt water via electrolysis. This reaction results in the formation of chlorine in basic and acidic analogs as sodium hypochlorite and hypochlorous acid, and these are used to sanitize the pool. Salt water pools can be a nice alternative to traditional chlorine pools, but they don’t feel like the ocean, since most residential salt systems require salt levels around 4200 parts per million, while the ocean has an average salt concentration of about 35,000 parts per million. 

Bromine is a relatively recent alternative to chlorine. It is similar in structure and behavior to chlorine but less pH sensitive, and it’s reaction in water leaves bromide salts in solution which can be recycled. The downside to bromine, however, is that it’s very unstable in sunlight. Chlorine will degrade in sunlight somewhat, but Bromine quickly becomes ineffective in direct light. This means that it can be used to sanitize indoor pools but won’t do much good if used outdoors. Concentration levels for most pools are similar to chlorine, as are the side effects and signs of overuse. 

Cyanuric acid is the solution to the instability of chlorine in strong ultraviolet light. The acid can be added to a pool to stabilize the chlorine in solution. It does this by binding to the sodium hypochlorite ions released by the chlorine after reaction with pool water, and shielding them from UV rays. This allows free chlorine to be effective approximately three times as long as it would otherwise be. Because Cyanuric Acid binds to active sites on the hypochlorite ions, it can decrease the active sites available for reactions with target pathogens, so levels that are too high will reduce chlorine’s effectiveness and may require fresh water dilution. 

Watersports anyone?

If there’s one thing divers are good at, it’s producing astonishing amounts of urine as soon as they put on a wetsuit. Unfortunately for us, neither dive equipment or urine reacts well with chlorine. There are no color-changing indicators to show who pees in a pool right now, but pee does react with chlorine to produce chloramines. 

Chlorine and urine, including their joint reaction, can be harmful to dive gear. Photo by GUE instructor Steve Millington, http://socalscubadiving.com.

This is a two-part concern for us, and serious enough that the CDC has to send out warnings every year. Pool urination simultaneously removes free chlorine from the pool, decreasing the pool’s ability to self-sanitize, and creates a chemical irritant called chloramines. The byproduct of the reaction of chlorine with the amines in urine, chloramines cause respiratory irritation, skin rashes and can irritate the eyes and mucus membranes. They also produce the smell we typically associate with over-chlorinated pools. 

As if that wasn’t enough, chlorine also degrades rubber like that’s it’s job. Black harnesses will fade to brown, o-rings and wing bladders will degrade, and regulators will need shortened maintenance intervals. Want to save your gear, your pool and your skin? Pee before you dive, rinse your gear well and keep that pool chlorinated. 

Want to save your gear, your pool and your skin? Pee before you dive, rinse your gear well and keep that pool chlorinated. 

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Reilly Fogarty is a team leader for risk mitigation initiatives at Divers Alert Network (DAN). When not working on safety programs for DAN, he can be found running technical charters and teaching rebreather diving in Gloucester, Mass. Reilly is a USCG licensed captain whose professional background includes surgical and wilderness emergency medicine as well as dive shop management.

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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