Here are a few items you can include in your logbook to help you stay organized and honest, track progress, and work on self-improvement as a diver.
I’ve had the good fortune to be in the company of some of the most respected overhead divers/instructors/instructor trainers spanning the globe.
Cave divers use a distinct set of markers to determine direction and distance traveled in a cave.
I constantly have to remind myself that gushing about my new dive toys to my friends at lunch will only be met with confused facial expressions, while discussing teenage gossip with a group of seasoned divers will have the same result.
by John E. Lewis, Ph.D.1:
This article could have dealt with Boyle’s law, partial pressures, oxygen toxicity, and how rebreathers work. Unfortunately, it would be three times as long and could (probably would) prove to be boring. Therefore, I chose a more direct approach. I have designed a single day of recreational diving and compared the experience of three divers equipped with different scuba devices ranging from a common open circuit aluminum 80 ft3 tank using air, an identical tank but one equipped with 32% nitrox, and finally the recently introduced Hollis Explorer semi-closed rebreather.
The Dive Scenario
The day’s diving takes place from a boat that is positioned in an area with a wide variety of depths ranging from walls with maximum depths over 30 metres / 100 feet to reefs as shallow as 18 metres / 60 feet. The Captain of the boat has decided there are to be three no-decompression (NoD) dives separated by two hour surface intervals and are to include a mandatory safety stop of five minutes at 3 metres / 10 feet. He also insists that the divers surface with no less than 35 BAR / 500PSI in their tanks.
This boat does not have a compressor, and it follows that all of divers must bring the tanks necessary for the three dives. The first dive is a multi-level dive beginning at 30 metres / 100 feet followed by a 15 metres / 50 feet second depth option. The second dive is also a multi-level dive to a maximum depth of 24 metres / 80 feet with a 12 metres / 40 feet second depth option. The third dive is to be at a single depth of 18 metres / 60 feet. In order to be able to visit the three sites that the Captain has chosen in the time allotted, he insists that for the first two dives the divers not exceed a 60 minute bottom time.
The Divers and their Equipment
Bob, by far the oldest of the three, carries on board three aluminum 80 ft3 tanks filled with air (21% oxygen). He has been diving for over 40 years, and he has developed the particularly low value of air consumption (SAC of 0.5 cu ft/min)2. Mike has three new aluminum 80 ft3 tanks that are prefilled with 32% enriched air mix and sport Nitrox labels. Ordinarily he has a considerably higher SAC, but for this exercise we have made his the same as Bob in order that we can see what Nitrox brings to the table. Nick, by far the youngest, has a brand new Hollis Explorer semi-closed rebreather that is equipped with a steel 28 ft3 tank filled with a 40% nitrox mix, and he too has two backup tanks similarly filled with 40% nitrox. Nick has a SAC of 0.75 cu ft/min, which represents a more common value among recreational divers.
All of the divers are equipped with dive computers, and with one exception, all have been programmed to reflect a predetermined value of oxygen content. The exception is Nick’s Explorer that has been designed to optimize the dive time by choosing a value of the oxygen fraction in the breathing gas such that the no-decompression limit (NDL) equals the capacity of the device. This of course is subject to the maximum operating depth (MOD) dictated by an accepted value of PO2 = 1.4 atm. In addition, the dive time based on the canister life of the Explorer is limited to 120 min.
The First Dive
The results of the first dive are shown in Table 1, where TBT refers to the total bottom time. The dive times that were controlled by NoD limits are labeled as ND, by scuba capacity as CAP, and 60 for the Captain maximum specified bottom time.
|Depth (fsw)||Bob (OC air)||Mike (OC Nitrox 32)||Nick (Explorer)|
|100||18 ND||30 ND||37 ND|
|50||22 CAP||12 CAP||18 (60)|
|TBT||45 min||47 min||60 min|
As can be seen, Bob, the traditional open circuit air diver, was seriously disadvantaged at the first depth of 30 metres / 100 feet where the other two divers have significantly greater bottom times. Note that if Nick with a more common SAC had been using the open circuit rig, his TBT would have been less than 30 min.
The Second Dive
After a 120 minute surface interval, the Captain has moved the boat to a new dive site where the maximum depth is 24 metres / 80 feet. Again Bob is at a disadvantage at the first stop. However, it is interesting to note that Mike who gained eight minutes over Bob at the greatest depth, lost five minutes in total bottom time. Nick with the Explorer greatly surpasses both Bob and Mike at the first depth even with the imposed 60 minute TBT.
|Depth (msw)||Depth (fsw)||Bob (OC air)||Mike (OC Nitrox 32)||Nick (Explorer)|
|24||80||30 ND||38 CAP||55 (60)|
|TBT||TBT||47 min||42 min||60 min|
The Third Dive
Finally the boat is anchored above a reef that has a constant 18 metres / 60 feet depth, and the Captain has told the divers that they no longer need to adhere to the maximum 60 min bottom time. All of our divers have switched to their clean tanks, and Nick has renewed the Explorer’s canister absorbent. The result is that with no constraint on bottom time, as can be seen in Table 3, Nick has more than twice the bottom time with the Explorer over the open circuit divers.
|Depth (msw)||Depth (fsw)||Bob (OC air)||Mike (OC Nitrox 32)||Nick (Explorer)|
|18||60||46 CAP||46 CAP||112 (IDEAL)|
|TBT||TBT||51 min||51 min||117 min|
We don’t see dramatic differences during the first two dives largely because of the boats 60 min bottom time limit. However, Mike by using Nitrox has had more time at the greatest depth as well as Nick using the Explorer. It is worth remembering that Nick has an average diver’s SAC of 0.75 cu ft/min whereas Bob, the elder, and Mike by caveat was granted the same low SAC rate of 0.5 cu ft/min. Finally, on the third dive where the Captain removed the 60 min bottom time cap, the Explorer had more than twice the bottom time as the open circuit divers. It is worth noting that while the Hollis Explorer is semi-closed, during the entirety of these dives the exhaled gas never reached 10% of that of the open circuit divers.
Based on this example, the Hollis Explorer rebreather has a significant advantage over open circuit divers even those with exceptional breathing control that is 2/3 the SAC of the average diver such as Nick. The Hollis Explorer is not accurately characterized as “no bubbles.” However, the undeniably aesthetic appeal of quiet that is less than 10% of open circuit divers is of considerable potential value to any diver in addition to the increased ability to interact with wild live.
In 1989, the term “dive computers” was first coined to describe expensive and exotic devices that were known by no less than 27 different names. Less than ten years later, the term was common place and the majority of divers dove with one. I will be surprised if another ten years go by before the same cannot be said of the expensive and exotic devices known as … rebreathers, and for recreational divers, rebreathers similar to the Hollis Explorer have the potential to be the standard for the future.
1This article is an updated version of an original article by the author that appeared in the magazine Discover Diving in February 1997.
2Surface Air Consumption
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:
- Create competent divers
- Allow the standards to be applied worldwide
- 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.
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.
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.
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 firstname.lastname@example.org.
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.
Don’t get lost cave divng. Read one man’s story about how he almost ran out of air cave diving.
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.
Isn’t it time you learned more?
Click Image to Expand
Perhaps one of the most common questions Technical Diving International’s (TDI) Training Department gets is “why do I need training for overhead environments?” While this question seems pretty obvious to TDI, we understand why it is not so obvious to the average diver. After all, you are breathing underwater, controlling your buoyancy and managing air just like you would on any other dive, right? Wrong. In this article we are going to focus on one specific type of overhead diving: caves.
Caves are one of the most fascinating environments a person can explore. Just think about it: these massive natural tunnels (some only a metre or 3 feet down) are below us, some dry some wet, while life on the surface moves along at its normal pace completely unaware that they even exist. These natural tunnels are responsible for a large portion of our drinking water and for moving water to the oceans or lakes to avoid flooding during rainy seasons and snow melt. Nearly every continent and country contains caves, most undocumented and unexplored. Some of these caves are just barely big enough for an adult to fit though while others are big enough to fit a descent sized town in.
While caves are undoubtedly fascinating, and there is clearly a need for them to be explored, they deserve a lot of respect and require specialized training before they are entered. Not all caves are made alike; some caves are low visibility with high water flow while others have clear warm water. Some caves are solid with no chance of the “roof” collapsing while others have what are called “breakdown rooms.” These rooms are where the earth above has been eroded to a point where it falls to the floor of the cave forming a large cone in the center; when this roof will fall is anyone’s guess. In some areas, even the caves that appear to be very stable are subject to seismic activity and could collapse.
The point here is that before entering any cave system proper training is required. Your TDI instructor, among other knowledge and skills, will teach you how the cave was formed and its stability. You will also learn things to look out for when planning a cave dive like “where do I look to find recent seismic activity so I know when it is safe to dive?”
Cave training is also a progression in training starting with caverns where you learn the basic techniques for deploying guidelines, buddy communication with lights and air management, all while staying in the ambient light zone. The next course is cave which takes you beyond the ambient light zone further into the cave requiring more air management skills and guideline techniques. The pinnacle of cave training is full cave; here you will learn complex circuits with jumps off the mainline and even more air management to allow for decompression dives. Please note: Decompression procedures is a pre-requisite for this course, decompression diving is not taught as part of the full cave course.
At any stage of your cave training you can add in other training such as: cave- diver propulsion vehicle (DPV), cave survey, sidemount or sump diving. There is a lot to do, see and learn just below the surface of the rock we walk on every day, but it requires some training from a TDI Professional. After this training you will be amazed at the exploration you will be capable of, and your friends will love the stories of your adventures.
So if cave diving is something you would like to learn more about, ask your local TDI facility or Instructor for more information. Our website is always a great place to start for additional information https://www.tdisdi.com, or simply give us a call at 888.778.9073 or 207.729.4201.