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When Easy Doesn’t Do It: Dual Rebreathers in Extended-Range Cave Diving

Rebreather technology has enabled cave explorers to extend their underwater envelope significantly deeper and longer. As a result, a few teams are pushing beyond the practical limits of open circuit bailout and so have turned to bailout rebreathers. But they are not without challenges, as Tim Blömeke, who dives into the latest research and field experience, explains.

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by Tim Blömeke. Lead image: KUR divers Bob Beckner and Derek Ferguson in the 124m/407 ft deep Mount Doom chamber in Weeki Wachee Spring, Florida, courtesy of Kirill Egorov.

Dual rebreathers are becoming a thing among the elite of extended-range cave diving. Yet the “Blueprint for Survival” for this type of equipment configuration has yet to be written, and practitioners are faced with difficult trade-offs between competing design goals—like fitness for purpose, logistical feasibility, simplicity, reliability, and ease of use, all of which interact with the peculiarities of human nature. A new research paper proposes a pathway for risk assessment. 

The introduction of rebreathers has considerably extended the range of exploration in cave diving. This is true especially for deeper dives, where open circuit technology faces the combined challenges of greater required gas volumes and higher required helium content, which make such dives both difficult to execute logistically due to the sheer number of cylinders involved, and prohibitively expensive due to the amount of helium in each of these cylinders.

By conserving the metabolically inert components of the breathing gas (most notably the helium), the use of closed circuit rebreathers (CCR) eliminates a good chunk of this problem, but not all of it: Traditional CCR diving procedures require that each diver have enough open-circuit bailout gas available to safely end the dive in the event of a rebreather failure. 

Granted, the amount of bailout gas required for a CCR dive is only a fraction of what would be needed to perform the same dive on open circuit, and if all goes well, the bailout gas will never be breathed by anyone and can be reused for future dives. However, bleeding-edge explorers being who they are and doing what they do, after having used their CCRs to push the range of operations a few miles deeper into the cave systems, they began to encounter an issue very similar to the one that prompted the switch to CCR in the first place: cost and logistics. 

As a real-world example, bailing out from a long-distance cave penetration of 7,500 meters at an average diver propulsion vehicle (DPV) travel speed of 40 m/min takes 187 minutes. Assuming a mean ambient pressure of 6 ATA (50 m depth) and a respiratory minute volume (RMV) of 14 l/min, the amount of bailout gas (not including decompression) required to reach the entrance would be 15,708 liters, or more than seven AL80 cylinders filled to 200 bar. This RMV is likely not conservative enough, given the extreme distance and the possibility of a hypercapnic event being the cause of the bailout so, in practice, a safety margin of at about 50% would be added, giving a total of 10-11 AL80 bailout cylinders. 

The required amount of bailout gas became too large to be carried on the person of the diver, so that cylinders again needed to be staged in a series of set-up dives. Preparations for extended range exploration dives became ever more involved, and logistics became just as difficult to manage as those of old-school open circuit dives–even more so, arguably, due to the considerably greater distance of the staging points from the cave exit. As happens so often, overcoming one obstacle resulted in the discovery of others further down the road.

Corroded stage cylinders.

New safety concerns started to appear as well: For large-scale exploration projects, bailout cylinders needed to remain in a cave system for months at a time, sustaining severe corrosion damage at the tank neck and tank valve interface in the process due to the galvanic reaction between the chrome-plated brass valve and the aluminum cylinder. This isn’t merely a hypothetical concern: On many occasions, the corrosion was so severe that the integrity of the seal was compromised, and explorers found their previously staged bailout cylinders empty when checking them on their way into the cave. While this can be counteracted by installing a magnesium anode on the cylinder (magnesium is lower in the Galvanic series than aluminum and replaces the latter in the reaction), explorers found that the countermeasure only mitigates the issue but does not eliminate it. Long story short, for extreme extended-range dives, open circuit bailout was becoming ever more impractical and problematic.

Enter The  Bailout Rebreather

As a solution to these problems, some explorers began to do away with open circuit bailout altogether and carry a redundant rebreather system—a closed circuit rebreather, or a semi-closed rebreather (SCR) instead. While this practice has gained significant traction recently, the concept itself isn’t new. In his book Into the Unknown, famed Welsh explorer Martyn Farr reports that his German colleague, pioneering cave diver Jochen Hasenmayer, had experimented with a dual unit he dubbed the Speleo-Twin Rebreather (STR-80) as early as 1981. 

Bill Stone flying FRED outside the Wakulla Springs decompression habitat. Photo courtesy of the US Deep Caving Team

In 1987, Dr. Bill Stone delivered a proof of concept by spending 24 hours underwater on a dual CCR, he dubbed “Failsafe Rebreather for Exploration Diving” (FRED), during his visionary Wakulla Springs Project 1987. However, it appears that the first person to utilize redundant rebreathers in actual exploration was Olivier Isler from Switzerland. On August 12, 1990, he first used a triple RI2000 semi-closed unit in his crossing of the Emergence du Ressel (Doux de Coly, France), covering a distance of 1850 m/6070 ft at a maximum depth of 81 m/266 ft. The following year, Isler went on to push through the 4000 m/2.5 mi penetration barrier for the first time. More than a decade later, in 2002, Reinhard Buchaly and Michael Waldbrenner pushed the exploration of the Doux de Coly farther using dual RB80s, which were originally designed by Buchaly and continue to be produced to this day by Halcyon.

Bill Stone spent 24 hours underwater on the fully redundant Cis-Lunar Mk 1, “FRED” during the at Wakulla Springs Project 1987. Here is Stone in the Wakulla deco habitat. Photo courtesy of the US Deep Caving Team

The decision to replace open-circuit bailout with a rebreather is as obvious as it is bold: Obvious because it replicates the successful solution to a past problem and restores the ability of a diver to carry all the gas they need on their person. Bold because… well. Put yourself in the drysuit boots of a cave diver, hours and hours away from the surface, who just survived an assassination attempt by a complex piece of life support equipment. All technical aspects aside, wouldn’t it be reassuring to fall back on a less complex piece of life support equipment whose proper functioning can be ascertained reliably within a few seconds? 

Olivier Isler sporting his triple redundant RI2000 SCR at Doux de Coly. Photo courtesy of O. Isler

Expressed in numbers, a paper by Andrew Fock, Analysis of recreational closed-circuit rebreather deaths 1998-2010, published in 2013, analyzed dive accident statistics for the period from 1998 to 2010 and found that CCR diving is associated with an increase in the risk of death by a factor of up to ten compared with open circuit diving. That ratio essentially applied to CCR dives, which used open circuit bailout. Rebreather technology and diving practices certainly have improved since the time under investigation, but the fact still remains that the complexity of the equipment adds to the overall risk.

With this in mind, taking a closer look at and trying to define the specific risks and benefits of replacing open-circuit bailout with a redundant SCR or CCR seems a reasonable idea. And this is precisely what a team of authors headed by Derek B. Covington did in a recent (March 2022) research paper, asking the question, “Is more complex safer in the case of bailout rebreathers for extended range cave diving?” 

Using a qualitative approach, the authors discuss the reasoning behind bailout rebreather use, its history, different configurations and the various advantages and disadvantages and, finally, the additional potential for human error created by increasing the complexity of the equipment.

Olivier Isler at a deco stop in Doux de Coly

Bailout SCR vs. Dual CCRs

In terms of configurations, there are two main choices for a bailout rebreather: SCR or CCR. With an SCR, the diver still has to carry bailout gas. However, an SCR (such as the side-mounted Halcyon RBK) extends the use of this gas by a factor somewhere between four and ten, thereby drastically reducing the number of cylinders needed while being only the size of a single AL80 cylinder itself. Other advantages of a bailout SCR are that its relative simplicity and lack of sensors or other electronics make it much easier to set up, maintain, and use than a secondary CCR.

These advantages, however, do not come without downsides. With an SCR, the diver does not have the option of adding oxygen into the loop, and the actual oxygen content of the gas breathed is always somewhat lower than the oxygen content of the gas in the cylinders carried. How much lower exactly depends on the portion of the gas vented into the water on each operating cycle of the unit—or the rate of fresh gas supply into the unit—as well as the metabolic needs of the diver. 

Therein lies the crux: For normal operation, the amount of oxygen consumed by the diver, and thus the resulting effective composition of the breathing gas, can be calculated quite reliably. In a bailout scenario, however, it isn’t unlikely for the metabolic needs of the diver to be increased due to higher workload. Without sensors to measure PO2, the precise composition of the breathing gas in the SCR loop becomes unknown, creating a risk of hypoxia, with all the potential consequences that come with it. This risk is unique to SCRs and not present when diving open circuit (where the cylinder sticker tells us what we’re breathing) or while on a CCR (where sensors tell us what we’re breathing).

The other approach is to go for a redundant CCR, as Stone envisioned back in 1987. While seemingly the “purest” in concept—replacing like with like—and optimizing redundancy, the added complexity is significant. Everybody who owns a CCR (especially an eCCR) knows that these machines need lots of love to remain in good working condition. Now multiply that by two: twice the number of sensors, two scrubbers, two sets of primary electronics, two sets of secondary electronics … and that’s just out of the water. 

Some open water explorers are also turning to dual rebreathers. Here is RAID president Paul Toomer in blue water wearing a back mount Divesoft Liberty with a sidemount Liberty bailout. Photo courtesy of Kristof Goovaerts.

To have the redundant system available to them at all times during the dive, divers now need to manage the contents of two breathing loops instead of one. Furthermore, in order to be able to provide assistance in the event of a problem, divers working in a team need to be aware of the failure modes of and emergency procedures for not only their own units, but also the units used by their teammates. Unless everybody on the team is using the same machines for primary and bailout, this considerably adds to the training requirements, as well as to the complexity of the decision-making tree in an emergency situation. Nevertheless, by maximally reducing the required amount of gas to be carried by each diver, a redundant CCR theoretically provides the greatest degree of independence and offers the greatest potential range of exploration.

Approaches to Risk Assessment

To date, the use of dual rebreathers is still too rare for a quantitative, empirical assessment of its safety to be practical, and there is no systematic process in place for collecting data on dual-rebreather dives. “It’s really almost impossible to put a number on it,” said researcher and explorer Andy Pitkin, who co-authored the study. “I think there are only a small number of divers in the world who really need a bailout rebreather, but there are probably quite a few who use them because the idea appeals to them more than using OC bailout. Of course, there is no hard dividing line between the two groups. Where does logistical difficulty become impossible? That’s a very subjective judgment.”

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The diversity of configurations and procedures used is another obstacle to objective study. “Are we using identical primary and bailout rebreathers, or is one unit specifically designed as a backup? If the latter, should the bailout unit be another CCR or an SCR? If the former, what are the diving procedures? Does the diver switch between loops at regular intervals, analogous to the procedures for independent doubles or sidemount diving? This would arguably add to task loading. Do the units have separate DSVs or a single, shared one, like that used by Richard Harris and Craig Challen of the Wet Mules? If the diver doesn’t alternate between units, then what other procedures are in place to ensure that both loops remain breathable at all times, especially during depth changes? If using dual CCRs, then what is the approach to ensuring redundancy of the diluent and oxygen supplies?”


The Wet Mules dual Megalodon CCR rebreather connected at the Bail Out Valve (BOV). Photo courtesy of Richard Harris.

The number of open questions and the range of possible, viable answers seem endless. Similar to the situation in the early days of cave diving, the book on bailout rebreathers has yet to be written. While many of the timeless principles from Sheck Exley’s famous booklet, Basic Cave Diving: A Blueprint for Survival continue to apply accordingly, there is no broad consensus yet on best practices, no SOP Manual, no standardized configuration, no published training standards for dual rebreather diving by any training agency. People are still working things out for themselves or their teams.

In consideration of these difficulties, and as a starting point for a discussion, the authors of Is more complex safer… propose a generalized approach to assessing the risks of dual-rebreather diving. Rather than delving into the minutiae of the failure modes of each individual diver’s equipment setup and diving procedures, they outline a method for identifying potential error-producing conditions (i.e., opportunities for human operators to make mistakes) based on a theoretical model originating in risk assessment for nuclear power plants: the WITH/TWIN model (Table 1). The acronym WITH stands for Workplace Design, Individual Capabilities, Task Design, Human Nature. TWIN refers to the same items (Task, Workplace, Individual, Nature).

The underlying idea of this approach is to move beyond merely looking at “human error” prima facie—oh, the diver failed to pack his scrubber properly? How could they! They neglected to monitor their PO2? Pay more attention!—and instead, analyze the conditions that are conducive to such errors. For the purposes of the model, a diver’s equipment configuration is part of their Workplace, their training and fitness belong in Individual Capabilities, the mission, including not only managing one’s gear but also navigation, linework, photography/videography, and surveying fall under Task. 

All these aspects interact with Human Nature. We get stressed when things get exciting, we get complacent when things go smoothly. We are prone to false assumptions, we are terrible at intuitive probability assessment, and our ability to pay attention falls off rapidly once the number of items that need our attention increases significantly beyond the number of voices in our heads. Much like running a nuclear power plant, excellence in cave diving isn’t achieved by sporadic strokes of genius but instead by consistently avoiding mistakes, and an important aspect of the design of equipment and procedures for either is to compensate for the inherent weaknesses of the human mind.

In the words of the study’s authors: 

“Divers and explorers need to consider not just the technical aspects of operating the dual CCR as an equipment-based system, but also the socio-technical aspects and error-producing conditions that adding additional complicated equipment has to the wider system, especially when it comes to training for and executing abnormal operations when workout levels will be high and awareness will be reduced. Nonetheless, as the use of this configuration grows, the risks and benefits will become clearer to investigators and divers alike.”

It will be exciting to observe the future development of dual-rebreather diving as it matures and see where the consensus for best practices will end up… stay tuned and stay safe!

References:

Diving and Hyperbaric Medicine: Is more complex safer in the case of bail-out rebreathers for extended range cave diving? Derek B Covington, Charlotte Sadler, Anthony Bielawski, Gareth Lock, Andrew Pitkin

Fock AW. Analysis of recreational closed-circuit rebreather deaths 1998-2010. Diving Hyperb Med. 2013;43(2):78-85.

NSS-CDS (free download): Basic Cave Diving: A Blueprint for Survival by Sheck Exley

Dive Deeper

InDEPTH: The RB80 Semi-closed Rebreather: A Successful Exploration Tool by David Rhea

Halcyon: Using The RB80 As A Side-mounted Bailout Rebreather by Andy Pitkin, Karst Underwater Research (2018)I

InDepth: Rebreather Holiday Shopping Guide (2020)

aquaCORPS Pioneer Interviews: Stoned: Interview With Dr. William Stone (1994) by Michael Menduno

InDEPTH: Diving Beyond 250 Meters: The Deepest Cave Dives Today Compared to the Nineties by Michael Menduno and Nuno Gomes

Deep Tech: Victory At Last (1998) by John Simenon: Olivier Isler is setting penetration records with a triple-redundant semi-closed rebreather


Tim Blömeke teaches technical and recreational diving in Taiwan and the Philippines. He is also a freelance writer and translator, as well as a member of the editorial team of Alert Diver. For questions, comments, and inquiries, you can contact him via his blog page or on Instagram.

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Hal Watts: Plan Your Dive

Known for his deep air diving exploits back in the day, 86-year-old Hal Watts, aka “Mr. Scuba,” is one of the pioneers of early scuba and credited with coining the motto, “Plan Your Dive. Dive Your Plan.” He founded the Professional Scuba Instructors Association International (PSAI) in 1962, which eventually embraced tech diving, but never relinquished its deep air “Narcosis Management” training. Italian explorer and instructor Andrea Murdock Alpini caught up with Watts and teased out a few stories from the training graybeard.

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Interview by Andrea Murdock Alpini 
English text by Vincenza Croce

Hal Watts, Terrence Tysall, and Bill Stone in March of 1993.  This was the last stop in the U.S. for a test dive of the Cis-Lunar Mk-4 rebreather prior to Stone’s San Agustin expedition (1994) for its first real sump dive.

“Plan your dive, dive your plan,” is a common refrain in diving, but it’s easy to forget the meaning of this phrase has changed over time.

The underwater explorers of the early days learned to plan their dives with watches, depth gauges, and US Navy tables. Back then, decompression tables were the Bible for divers—something miraculous, halfway between alchemy and physiology. Those trail-blazing divers defined what it meant to “plan” a dive.

But, at the time, the term “technical diving” did not exist; divers breathed air on the bottom as well as during decompression. Only after many years was oxygen added, followed by the famous jump into the hyperbaric chamber.  

Later came new innovations after a few decades of experiments: hyperoxygenated binary mixtures, the NOAA tables, Heli-air (i.e. the addition of helium in tanks loaded with air), the change in the speed of ascent, new molecules to be studied, new physiological and narcotic effects, and their consequent impacts on humans and their psyches.

In a very short time, diving traditions underwent a metamorphosis. The spool and the coral tank became a proper reel, the ascent bin and the plastic bag disappeared in favor of the buoyancy control device (BCD), the surface marker buoy appeared—and then, even later on, wrists were adorned with underwater computers instead of decompression slates.

Divers later renewed and revolutionized a niche discipline, transforming it into a sporting phenomenon and a vocation. Faced with imminent change, there is often nothing that can be done when an anomalous wave arrives; you cannot stop its irresistible force with the wave of a hand. And thus was the American revolution of underwater technique, where the means of exploration—read mixed gas and scooters—have become the end.

The self-proclaimed originator of the “plan your dive, dive your plan” motto was 86-year old Hal Watts, the founder of American didactic Professional Scuba Association International (PSAI) and a diving pioneer who once held the Guinness Book of World records for deep diving. Though the use of trimix grew in popularity, Hal continued to believe in deep air, in the ancient technique of coral fishermen. He supported wreck and cave diving—with decompressive mixtures and new configurations through PSAI; but, above all, he believed (and continues to believe) that deep air, if properly practiced, is a discipline with unique logistics, hidden dangers, and irresistible charms that can take you to a parallel world.

Hal Watts speaking at aquaCORPS tek.93 Conference

First of all, Hal, what was the dive that changed your way of seeing scuba diving? I mean, a dive that was like an epiphany, a dive which changed your point of view on a technical matter?

Hal Watts: Wow, you sure are really trying to test my old man memory. Now I’ll have to review some of my old logbook entries. 

The first scuba dive that really got my attention as to just how serious and dangerous scuba diving can be was on December 2, 1962. I was diving with Bob Brown, co-owner of Florida State Skindiving School in Orlando, Florida. I was a member of a dive club in Orlando known as Orlando Sport Diving Club. Bob and I had heard of a sinkhole in Ocala known locally as Zuber Sink as well as Blue Sink. Years later, I later leased the property and renamed it as Hal Watts’s 40 Fathom Grotto, and I eventually purchased the Grotto in mid-1979.

We had never talked to anyone about the sinkhole; therefore, we had no idea about the visibility or the depth. Up to this point, I had constructed my favorite BCD, using a large white Clorox plastic jug, which we tied to our twin tank system. We put air into the BCD from our “Safe Second Stage” mouthpieces. 

Bob and I tied our safety line to a tree on the bank of the sink and reviewed our dive plan. I am reminded of the motto I came up with, many moons ago—Plan your dive, dive your plan. 

We all know that motto. I didn’t realize that it was you who coined it.

It was back in the 1960s when I was writing course manuals for NASDS [National Association of Scuba Diving Schools] and opened up my Mr. Scuba dive shop.

Mr. Scuba’s Magic Bus!

But back to the dive at Zuber. I’ve failed to mention the fact that neither of us had been doing any dives below 30 m/100 ft. We followed the cave line down slowly, not paying enough attention to our depth. Before we realized it, we had hit the bottom, stirred it up, and had no clear water.

Lucky for us, I kept the cave diving reel in my hand, and Bob kept his hand on the line. I couldn’t see; however, I could feel Bob’s hand, squeeze his fingers tight on the line, grab his thumb, and give it the “thumbs up” signal. I don’t know how we managed it, but we were both able to use our NASDS safe second stages and add air into the Clorox “BCDs.” We were actually fated to begin an uncontrolled, too-rapid ascent. All of a sudden, we hit an overhead wall, which stopped our ascent at a depth of 9 m/30 ft. 

We looked at each other, and gave the OK hand signal. While decompressing, following the old Scubapro SOS mechanical computer, I started to pull up the loose line until the dive reel appeared. Wow, we sure had an awful lot of loose line floating around us. Were we extremely lucky? Of course, we were. Our problem was that we never planned our dive, and consequently, were unable to dive a plan.

After that dive, I worked with Scuba Pro and Sportsways to create the “Octopus,” or “safe second.” A while later, the octopus appeared for the first time in Scuba Pro catalogs. I was also the first to add a pressure gauge along with the Octopus.

Hal Watts set the world deep air record to 120m/390 ft in 1967

Ah yes, the “Safe Second.” That’s what NASDS called backup second stages, right? Sheck Exley (1949-1994), the legendary cave explorer with whom you were friends, was also credited with fitting a redundant second stage reg with a necklace. I want to ask you more about Exley, but first, I want to know: What are the best wrecks you ever dived?

This is really very hard to answer. I’ll have to list four, in the order that I dived them: the USS Monitor, Andrea Doria, Japanese wrecks located in Truk Lagoon, and the Lusitania in Ireland.

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The most important would have to be the USS Monitor, a submarine used during the Civil War. A group of well-known USA divers applied to the National Oceanic and Atmospheric Administration (NOAA) for a permit to dive the Monitor, as she was located in protected waters. In addition to myself, the group consisted of: Gary Gentile, attorney Peter Hess, and several other well-known expert divers. At first, NOAA refused. Then, Peter Hess filed proper papers asking that we get the NOAA permit. To that end, we presented my Deep Air training material to the concerned NOAA group. I appeared as an expert witness and provided NOAA staff and their legal representatives with my internationally accepted training material and my record of training several world record deep air divers. Our deep air training has been accepted worldwide with zero diving deaths. After that, we received the permit. 

Other than the Monitor, my favorite deep wreck dive would be the Lusitania, which is a very personal and proud story for me. The main reason is because venture capitalist Gregg Bemis owned the diving rights to the Lucey at the time. Gregg had contacted me requesting that I train him on PSAI Narcosis Management Level V, on air—which is 73 m/240 ft—and then train him on trimix so he and I could dive to 91 m/300 ft on the Lusitania lying off the coast of Ireland. 

When word got out that I had enrolled Gregg in my Narcosis Management Course, a well-known international course director (a personal friend of mine) called and told me, “Hal, do not teach Gregg deep diving.” 

PSAI’s ad in aquaCORPS Journal circa 1994 offering deep air training.

He told me that he had been training Gregg at his facility, and that he was a “train wreck.” “He is from a very well-off family in Texas, and if you cause him any injuries, you will be sued and put out of business,” my friend said. Well, guess what? Gregg completed the 240 Level V Deep Air course, then our PSAI Trimix course. My wife, Jan Watts, Gregg, and I went to Ireland to dive the Lusitania. He and I made an awesome 91 m/300 ft trimix dive to the deck.

Diving on the Andrea Doria with Tom Mount, Peter Hess, and several great wreck divers was also an awesome dive. Last but not least was a great trip to Truk to dive on some of the Japanese wrecks.

Please tell us about Sheck.  What was your relationship with him like?

Sheck and I became friends and made several dives together, and one of my favorites happened when Sheck, his Mary Ellen, my wife Jan, and I were diving at 40 Fathoms. Sheck wanted to practice gas switches during descents. Sheck was practicing, getting ready for a planned very deep dive (I think in Mexico with Jim Bowden). The four of us swam to the east side of The Grotto, slowly following the wall during our controlled descent, watching Sheck practice gas switching. 

Sheck Exley and Hal Watts at a NSS-CDS conference

After reaching our planned depth of 73 m/240 ft, we began our controlled ascent up to our first planned deco stop. During our last deco stop on our 4.5 m/15 ft platforms, I noticed that Sheck had a funny look on his face and was messing with his drysuit between his legs. I remembered then that he had told me that he had an attachment installed in the drysuit that would allow him to pee underwater. He was clearly in a bit of discomfort and Mary Ellen, Jan and I just floated nearby and watched.

I’ve heard that Sheck later used diapers, or just cut it loose in one of his old neoprene drysuits on his big dives, so evidently he didn’t get that early p-valve to work. What about your friendship and job collaboration with Gary Taylor, your brother-in-arms and a co-owner of PSAI?

Andrea, get comfortable, since this question will take some time to properly answer.

I first met Gary in Miami, which is where we became friends when I was staying in his home and taking Tom Mount’s nitrox course.  I have a photo of Tom, Gary, and me gas blending on the floor of Tom’s garage. During the course, Tom was still using his worn-out hand written paper flip charts as his notes.

Gary was impressed with my deep air program and offered to put together an updated slideshow presentation for me to teach with. PSAI still uses an updated version of this system to date. Gary stayed with Tom until Tom thought he had sold IANTD [International Association of Nitrox and Technical Divers] to another individual. After that sale came about, Gary contacted me wanting to get more involved with PSAI. Being smarter than folks thought I was, I jumped at the chance to have Gary on the PSAI Team. Tom’s deal fell through, but Gary was totally involved with PSAI, and now is a partner and president of our agency. Thanks to Gary and Tom. 

Many, many years ago I was still taking some type of classes—I think regarding mixed gasses, maybe with Rebreathers—at Tom’s house. In fact, I was one of Tom’s instructors who did the final proofreading of one of Kevin Gurr’s manuals. Too far back to recall much about this mixed gas stuff—remember my reputation for being a deep air diver.

Tom Mount and Gary Taylor mixing up some trimix in the garage.

Speaking of the people with whom you’ve dived, was the aim of The Forty Fathom Scubapros Club?

Before I invested in a sinkhole in the Ocala, Florida, area—which was locally referred to as Blue Sink or Zuber Sink, and is now referred to as 40 Fathom Grotto—several diving buddies whom I had dived with and trained for extreme deep air diving—as well as cave exploring—got together and planned to dive The Grotto at least one Friday night per month. Within a short period of time, several other buddies joined our group, which eventually became known as The 40 Fathom Scubapro’s dive club. Each diver had to meet my requirements of training. 

Forty Fathom Grotto aka Zuber Sink
An early Sheck Exley mix course at Forty Fathom Grotto
An Eric Hutcheson drawing of Forty Fathom Grotto

Eventually, our group set specific personal requirements—being a good person, supporting our club safety rules, and making at least one 40 Fathom Grotto dive per month. We set a limit of 14 or 15 members. Three 40 Fathom members eventually set World Records for deep air: I was one, A. J. Muns, and Herb Johnson set ocean records, and later I set the air depth record for cave diving. Naturally, as time passed and we got older, our membership got smaller. It is notable that none of our club members have died during any scuba dive.

Finally, what led you to create the iconic motto, “Plan Your Dive. Dive Your Plan?” 

I used to be a private pilot, and we used to say, “Plan your flight, fly your plan.” This was back in probably 1961 when I had just started diving and there were so many instances where all the other divers would get in the water without saying anything. I’ve seen so many incidents and fatalities that could have been avoided through proper planning.

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Dive Deeper

ScubaGuru: LXD 029 : Hal Watts – Record Deep Diver & Technical Diving Pioneer

Netdoc: Netdoc chats with Mr Scuba, Hal Watts

InDEPTH: The First Helium-based Mix Dives Conducted by Pre-Tech Explorers (1967-1988) by Chris Werner

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

Professional Scuba Association International: PSAI History


Andrea Murdock Alpini is a TDI and PSAI technical trimix and advanced wreck-overhead instructor based in Italy. He is fascinated by deep wrecks, historical research, decompression studies, caves, filming, and writing. He holds a Master’s degree in Architecture and an MBA in Economics for The Arts. Andrea is also the founder of PHY Diving Equipment. His life revolves around teaching open circuit scuba diving, conducting expeditions, developing gear, and writing essays about his philosophy of wreck and cave diving. He published his first book, Deep Blue: storie di relitti e luoghi insoliti (2018) and IMMERSIONI SELVAGGE, the new one is on the way, out on fall 2022. 

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