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cave_rebreather

Is Cave CCR the Ultimate Challenge in Diving?

by Steve Lewis:

rebreather in cave

As if cave diving isn’t challenging enough, how should we feel about adding a rebreather to the mix?

When asked, which happens from time to time, I’ll explain to anyone who’ll listen that the easiest way to really give your diving skills a workout is to enroll in a cave diving class. The customer feedback from folks, who take this piece of advice, and dive into a technical overhead program, usually makes extensive use of the words “humbling” and “embarrassing”. The phrase: “brought me down a peg” or something similar often makes an appearance too.

Cave diving, and to some extent Advanced Wreck Diving (i.e. wreck penetration), is fundamental to technical diving. Most of the information covered and the majority of skills and techniques taught in any technical diving program have their foundations in basic cave diving. The presence of a rock ceiling, rock walls, and a rock floor (often covered in a deep layer of fine-grained mud) tends to focus the mind and put a special meaning and strong emphasis to the sage advice that bailing out to the surface is not an option. As any technical diver will tell you, it’s very unwise to bolt for the surface on any dive, especially one that’s incurred a decompression obligation, but in a cave several hundred metres or feet from open water, that option is completely off the table. Problems of all shapes and sizes have to be fixed at depth.

One result of not being able to surface at will, is the cave diver’s conservative approach to gas management: specifically, carrying enough gas to get them and a buddy back to safety in the event of the most horrendous equipment malfunction at the back of the cave. The Rule of Thirds, the starting point from which cave divers traditionally begin their gas volume calculations, is the ubiquitous gas management technique adopted by virtually all technical divers.

Also, the techniques developed and refined by cave divers operating in North Florida and the Caribbean for communications, propulsion, equipment selection and configuration have to a great extent become the best-practice defaults for almost every technical diver around the world.

Furthermore, it’s long been accepted that the standards required for cave instructors (and their students) to earn their certifications to teach (or dive) in caves, are among the most stringent. Broadly speaking, the consensus is that cave divers and the men and women who certify them, are among the most meticulous and squared away of any group of divers.

So, what happens when we take the rigors of a cave diving course and apply them to a new program for which the core life-support systems have been changed from open-circuit to closed?

To begin any comparison, it’s fair to say that TDI’s training department and advisory panel thought long and hard about the best ways to evolve its successful cave diving curriculum to include the special needs of closed-circuit rebreather diving. I was not at head-office for the whole of the development process, but I know it was the work of a larger development team than any previous program. Which is hardly surprising given the magnitude of responsibility to “get it right” when combining the complexity of a rebreather with a supremely challenging underwater environment. Hardly surprising and somewhat comforting!

Given that, let’s look at what they came up with!

The basic shape of most cave courses is the same regardless of what type of gear the diver opts to use. The first step is Cavern Diver. Graduates from Cavern can move up to Intro-Cave Diver; and once that level is achieved are able to sign-up for Intro to Cave and Full Cave courses.

In the briefest of terms, cavern divers are severely limited in where they can venture; intro-cave divers have to stay on the permanent main line or gold line and are not allowed to make any jumps to side passages; and full-cave divers have a license to learn in most of the cave’s main and secondary passages.

The progression has stood almost unchanged since the first organised cave diving programs that pre-date the formation of most of today’s mainstream certifying agencies… in other words, it’s a progression that’s stood the test of time and held its value well. It then follows logically that TDI’s CCR Cave program follows this same structural paradigm.

WHAT’S A CAVERN?
I don’t think there’s any real confusion about where open water ends and a cavern begins: if you cannot swim straight up to the surface and fresh-air, you’re in an overhead environment. If the ceiling is wood or metal, chances are that you are inside a wreck, and if the ceiling is rock, you’re in a cavern.

There might be more confusion about the other end of the cavern and where exactly it turns into a cave.

The standard definition is that the primary source of light in a cavern is daylight. If you and I swim into a cavern and lose sight of the entrance and daylight, we have exited the cavern zone and entered the cave proper. And for the record, there are no caverns at night… and some cave systems do not have a cavern zone to speak of at all. (The Eagles Nest system in Florida as an example.)

That definition does not change for rebreather divers, but there is a subtle change that fundamentally sets up one of the challenging limits for overhead training on any CCR.

One absolute limiting factor for all open-circuit divers is the volume of gas they and their buddy or buddies are carrying. That volume (X litres or Y cubic feet) helps to define just how far they can travel into an overhead environment… given that they follow the established guidelines for gas volume management.

In TDI’s open-circuit (OC) cavern course, penetration is limited to one-third of the volume of a single diving cylinder or one-sixth if the divers are using double cylinders. This is somewhat further defined to explain that the available volume for penetration for the whole dive team is set by the team member with the smaller cylinder or who has the smaller(est) starting volume.

The same volume limit is suggested for OC intro-to-cave graduates.

This limit very effectively helps to “police” or control new cave divers’ return access to open-water and safety. Since running out of gas is #1 on the list of things to guarantee a cave diver is going to have a bad day, the one-third in a single / one sixth in twins guideline goes some way in keeping new cave divers from venturing too far into the cave.

But a fully functional CCR does not have the same sort of built-in restriction. Certainly both diluent and oxygen supply is limited but those limits are measured in hours rather than minutes.

Let’s take the oxygen supply as an example. (Forgive the use of SI units but cubic feet are more complicated and unnecessary to get the point across. If you are only used to American Customary Units, just think of litres as quarts.)

We’re taught that the average per minute oxygen consumption rate for a diver is 1.5 litres. This volume is depth independent. And unlike their OC breathing brother and sister divers, for a diver on CCR, it really makes little difference whether the consumption is measured on the surface or at advanced trimix depth. One’s consumption rate will vary a little with workload, but 1.5 litres makes a pretty good average to work with. For now, let’s make life simpler and a tad more conservative, and use a consumption rate of 2.0 L/min. This is really quite high, but two litres a minute makes the arithmetic even easier than it would be at 1.5.

Now the smallest rebreather tank in common use has a wet volume of about two litres. That means every full atmosphere of pressure in that tank equals two litres of gas. In other words, a fill of 200 bar means there are 200 X 2 litres of gas. That’s 400 litres of gas. Quick math… at two litres a minute consumption, this volume of gas will last up to 200 minutes!

Even if we follow a sort of rule of thirds and suggest a CCR diver only use one-third of his or her starting volume of oxygen, one third of 200 minutes is more than an hour.

This means that if a beginning CCR cave diver follows the same gas rules as an OC diver, he or she can swim into the cave for an hour before having to turn the dive on gas volume! An hour of swimming into a cave usually translates into about an hour swimming out. Sometimes the flow helps to make an exit a little shorter, but an hour would be a fair estimate.

I think even those of us who have zero cave experience will begin to see the potential for a huge problem with this scenario.

If we were to line up the special concerns of those who teach CCR cave diving, at the front of the queue would be: a rebreather is essentially a potentially wicked cross between a time machine and a gas extender. What makes it potentially wicked is that compared to the classic North Florida set of twin steel tanks (even the big ones) the most inexperienced diver can wander deeper in to a cave system… much deeper than he or she should. If something bad happens, an hour is a long swim nursing a problem.

The “magic bullet” designed to help avoid this type of event centers on bailout gas.

Bailout gas is what a CCR diver carries for contingencies. Should the rebreather become completely inoperable, then they stop using it and start breathing from a tank of compressed gas using a scuba regulator. In other words, they fall back on good old-fashioned open circuit.

Some time is spent in the foundation dives for cavern and intro-cave CCR programs working out how much bailout gas each diver must carry, and how far from the surface that gas allows them to venture.

The calculations for this distance are based on a consumption rate effected by a carbon-dioxide breakthrough on the rebreather. A breakthrough such as this would probably result in a diver breathing like a racehorse on the final furlong of the Preakness. Therefore, the calculations are conservative and the guidelines they offer for penetration are written in stone: a sensible diver would never dream of compromising his safety by ignoring these guidelines.

Is your head spinning yet?

The truth is that the task loading for a student taking a CCR Cave class is really high. In addition to the gas management “thing” they have to master all the skills expected of an OC cave diver. They have to run line, place line markers, read the cave, overcome current, learn navigation, perform lost line drills, lost buddy drills, show their instructor perfectly executed bottle swapping in zero vis, and prove they can swim without kicking up a curtain of silt. And when that’s finished, they need to come up with strategies for rebreather-specific issues. They have to run their CCR manually, in SCR mode, they have to deal with depleted diluent, low oxygen, stuck solenoids, and a raft of other “fun” challenges!

Is your head spinning now?

The truth is that I dive CCRs in caves by choice. I believe that all things being equal, a rebreather is the right tool for cave exploration eight times out of ten. (Sidemount covers the other 20 percent!) Like so many high-risk activities, the pay-off is high-value. It’s also a class I love to teach because it is such a challenge and students walk away with a justified sense of accomplishment.

Is Cave CCR the ultimate challenge in diving? I know Brian [Carney, president of TDI] and the team in TDI’s training department well, and I am sure they have other cards up their sleeve; but as it stands, I cannot think of another program that tests a diver’s mental and physical stamina more than this course.

Is it fun? Yes it is. Is it useful? Certainly. Is it tough? Sure thing. Should you start planning to challenge yourself? Well, I don’t know if you’re ready but if you think you might be… Go for it!

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Cave Diving Course – Behind the Scenes of the Rebreather Cave Course

Our membership has been hounding us for years and we’ve finally got it finished, The Rebreather Cave Diving program is here and we are extremely proud of the final product.  When we create a new course we have 3 goals in mind:

  1. Create competent divers
  2. Allow the standards to be applied worldwide
  3. Make sure the standards are insurable

As you can imagine successfully accomplishing these three goals with a program as involved as training people to dive in caves using rebreathers was extremely difficult, but we were up for the challenge.

cave_diving_course_1

How it all got started: 

In the past TDI had distinguished that rebreathers were an equipment configuration and caves were an environment.  We allowed cave/rebreather instructors to teach their cave courses utilizing rebreathers but did not have any specific standards for this type of training; instructors were simply allowed to teach the cave courses using the rebreather as an equipment configuration.  This worked well for a while, but had a few obvious drawbacks including: gas management, bailout requirements, and out of air drills.  The skills for managing many of the aspects of diving a rebreather in a cave are significantly different than diving open circuit. We found that we needed to address these issues.  In 2010 a TDI Instructor Trainer, who is also a member of our Training Advisory Panel (TAP), wrote a unique specialty to address these issues.  He created a program specifically for diving closed circuit rebreathers in caves, from a basic cavern level up to an advanced mixed gas level.  This course has been very successful for him and he has even trained several other instructors to teach his program as well.  He has been training extremely competent divers, and we have been receiving rave reviews about his courses.  After running this program successfully for the past two years we decided to create a global standard using this unique specialty as our foundation.

Why did it need to be changed?

If you have ever met a cave diving instructor, you would probably agree that they tend to have pretty strong opinions about how things need to be done.  While the main focus is always training the most competent divers possible, the route to getting there can vary significantly from instructor to instructor.  While we had a great foundation already in place, the rebreather cave program that was being taught was written specifically for one instructor’s teaching style, philosophies, and the environment he was typically teaching in.  We decided to reach out to a few other members of our TAP (some of the most experienced cave and rebreather instructors on the planet) and see what they thought.  Just as expected there were many heated emails exchanged and at times it seemed we would never come up with a solution everyone could live with.

Now what?

It wasn’t until we sent two TDI training department staff members into the field for some hands on testing that we started to make significant headway.  Already experienced advanced mixed gas rebreather divers but not yet cave divers; they were perfect candidates for this type of research.  They dedicated most of their weekends for almost 3 months to the project, spending over 20 hours underground in the springs of North Florida with one of the world’s most accomplished cave instructors (rough life, right?).  Through hands on experience and the help of TAP members around the world the rebreather cave diving program was shaped and molded. The result is a set of courses, Rebreather Cavern, Rebreather Introductory Cave, and Rebreather Full Cave Diver, that can be adapted by a wide variety of teaching styles and environments to produce some of the most competent rebreather cave divers in the water.

Launch Time.

Now that the standards are written, it’s time to get the course out to the public.  We have chosen several instructors and instructor trainers around the world to begin offering the TDI Rebreather Cave Program and are excited to start training rebreather cave divers.  For a list of instructors and instructor trainers or for more information on these courses please contact us at worldhq@tdisdi.com.

Thank You.cave_diving_course_2

This project was a huge undertaking, and there’s no way we could have done it on our own.  We would like to give a special thank you to Ben Reymenants, the author of the original CCR Cave unique specialty outlines; without this foundation we would have had to start from scratch.  Ben continued to provide TDI with feedback on how his courses have been going as well as provided feedback from the CCR Cave Instructors he had created using his unique outline.

Also, thank you to Randy Thornton and his sons, Josh and Michael, of Dive Addicts in Draper, UT.  The Thornton’s are very active instructors and instructor trainers, specializing in rebreather and cave training.  The input they provided was priceless, and always seemed to be the nudge that we needed to keep moving forward.  Sorry it’s taken so long guys, but we would still be far from finished if it weren’t for your help.

Finally, thank you Lamar Hires, owner of the equipment manufacturer Dive Rite, for providing much of the equipment used and so many hours of his personal time to work with Jon and Lauren Kieren of TDI for their rebreather cave training.  Lamar is an icon in the cave diving world and his never tiring dedication to the dive industry and the improvement of training proved to be an invaluable resource for creating the Rebreather Cave Diver courses.

Interested in the Rebreather Cave Program?

Diver Level Courses

Instructor Level Course


Contact SDI TDI and ERDI
If you would like more information, please contact our World Headquarters or your Regional Office.

Tel: 888.778.9073 | 207.729.4201
Email: Worldhq@tdisdi.com
Web: https://www.tdisdi.com
Facebook: https://www.facebook.com/TechnicalDivingInt

divers_diary

A Divers Diary of the TDI Rebreather Cave Diver Course

divers_diary

Photo credit Peter Lapin

Over the past few months, two members of the TDI training department spent their weekends assisting in the development of the Rebreather Full Cave Diver course. As CCR Advanced Mixed Gas divers with years of deep ocean experience and zero overhead environment training; they were the perfect candidates to test and challenge this course in the making as real students with one of the most experienced cave instructors in the field.

After 20+ hours underwater, a lot of lessons learned, humbling and exhilarating moments and more; they completed what is now the TDI Rebreather Full Cave Diver course. To recap on those experiences, here are some highlights from their course:

Day 1: Land Drills – After learning how to properly deploy and follow a guideline, our instructor set up a triangular course for us to follow in the woods. We tracked the guideline several times over with different variables in play each time around. The first time through the course we were able to have our eyes open and simply walk next to the line, easy enough right?  This drill eventually progressed to closing our eyes while keeping in contact with the guideline and each other. The last time around the course with these variables in play it took us well over three times as long compared to the first time around. I don’t think I will ever forget our instructor’s face when he said, “you both are dead.” Ouch!

This drill was used as an example of improper dive planning.  If we planned our bailout gas requirements based on the first time it took us to track the course (in easy conditions) and something went wrong (leading to a challenging exit), we would have exhausted our emergency bailout gas reserve before exiting the cave. First lesson of the course: Expect the unexpected and plan for the worst case scenario. Caves are an unforgiving environment; when things go wrong the potential for a continuous downward spiral is always present and you might be faced with little or no options if you do not plan your bailout accordingly.

Cavern Dives The first few dives we made in the course were conducted in the cavern zone.  This was our first experience applying the land drills we conducted earlier that day.  Line laying, gas sharing, and zero visibility scenarios were played out extensively until our instructor was confident in our ability to handle these stressful situations.  These were possibly some of the most humbling experiences of my diving career.  Going into this course I thought I was a pretty good diver capable of handling a lot in the water. At this point, I realized I was truly a novice in this new environment with a lot to learn.  This was certainly going to be an interesting course…

First Cave Dive “I need to get in better shape.” During our first swim beyond the daylight zone of the cavern going into the darkness of the cave, I felt the outward flow of water seek to push me out as I was striving to swim in. Although this makes for an easier exit, it created a very wearing entrance. I was trying to recall all of the things our instructor said about body positioning in the water, learning the cave’s personality, and tucking behind rocks or the diver ahead to “draft” them. None of it seemed to be working; I was tired, frustrated, and my ego was about the size of a pinhead at this point.

Working hard and over-breathing is not a good recipe on a rebreather. I knew I had to take a break to collect myself and gain control of my breathing rate before progressing on at a slower pace. I spent the rest of the dive observing my instructor’s movements while trying to get a feel for moving efficiently in the water. My technique was improving but I was lacking speed and stamina.  I knew I was in need of a lot of work to keep up in this environment.

That was the last dive for the weekend and I left with a goal in mind; get in better shape! I spent the next three weeks out of the caves and in the gym. The only diving I did during that time was in shallow water practicing skills and line laying drills for the dives to come.

1st half of the course “A rebreather is a tool, utilize it!” Throughout the course, we practiced a number of skills and drills to make the most of a rebreather in the cave environment. Even though you must always properly plan your bailout requirements for the dive to allow a safe exit, with proper training and execution, diving a rebreather sometimes offers other options in adverse situations.

We spent the majority of these dives practicing and perfecting these options which include but are not limited to; flying the rebreather manually, semi-closed rebreather mode, bailout bottle swapping exercises, and more.  The first half of the course also included a lot of lost diver and lost line drills.  We exercised these drills on almost every dive until we were comfortable quickly deploying our safety reels and conducting a quick search for either a simulated lost teammate or the main line.  These drills were a good reminder of how great a rebreather is for the cave environment.  In the event you lose the mainline or a teammate, you have time to conduct an efficient search without having to worry about a quickly depleting gas supply.  While we were starting to feel comfortable in the cave, there was still a lot of work to be done.  At one point my teammate mentioned, “I feel just comfortable enough to get myself into some serious trouble.” Meaning he was comfortable in the environment, but knew he had a lot left to learn.

2nd half of the course “I am starting to get the hang of this…” After three months of a new workout routine, a fair amount of time in the caves, countless skills & drills; our overall comfort and confidence in the cave environment increased.  We were now working on complex navigation in the cave, making multiple jumps off of the main line and doing large circuits and traverses.  We were moving quickly and efficiently in the water for extended periods of time without getting tired and our skills were on target but we still didn’t quite have “it” yet…

Our instructor placed a major emphasis on situational awareness in the cave. The reoccurring question of the course was “what is your swim rate?”  If we couldn’t answer that question appropriately, we typically received a “come on guys, you have to know your swim rate” lecture. The reason why it’s important to know your swim rate is to track the amount of time it takes you to swim a certain distance given the environmental factors (i.e.; high flow, low flow, and siphon). You can track this by monitoring a timing device as you pass each line marker indicating penetration distance. On a rebreather, you don’t always have your gas supply to tell you when to turn around. A rebreather enables a diver to spend a vast amount of time in the water; this can be deceiving in the cave environment if you venture too far in without adequate bailout to exit if something goes wrong.  Often times you have to use time and distance to judge your turning points.  If you go beyond the range of your bailout you can end up in a seriously problematic situation.

Last Cave Dive“We finally figured out what “it” is…”   As we were making our way into the cave I noticed we were swimming at a rate of 80-100FT/minute. I knew we made substantial headway in swimming rates since we started the course however, 100FT/minute was not a realistic pace given the limited amount of work we were putting out. As we were nearing the point we designated as our turn around location, we decided to call the dive a little earlier and make our way out. As we were exiting the cave, we noticed our swim rate slowed down to 50-60FT/minute, meaning we were moving at half the pace and would exit in double the amount of time it took us to enter the cave.

Once we surfaced our instructor asked why we called the dive earlier and if we noticed anything different. After indicating that it was a siphon, noting our exact swim rates, and the reason why we turned sooner was to allow extra time for our exit; he finally smiled and said “you got it.”

After completing the TDI Rebreather Full Cave Diver course; experiencing some of the most challenging, humbling, and exhilarating moments in my dive career, I can honestly say I can’t wait for more. The amount of dive experience my teammate and I had prior to the course could not prepare us for this type of diving. Now it’s time for us to keep our skills fresh, stay current, and slowly gain experience in the caves.

Contact SDI TDI and ERDI
If you would like more information, please contact our World Headquarters or your Regional Office.

Tel: 888.778.9073 | 207.729.4201
Email: Worldhq@tdisdi.com
Web: https://www.tdisdi.com
Facebook: https://www.facebook.com/TechnicalDivingInt