Origin of Rebreathers & Underwater Warriors

by Mark Phillips:

LCOC unit approaching beach

photo credit: www.history.com

War is one of mankind’s greatest failings and perhaps one of the greatest instigators of invention.

In war men fight. Ships sink. When men learned how to extend their time underwater to salvage sunken vessels it was their nature to consider the concept of an underwater warrior. Those soldiers would have to be comfortable in most any condition of water. They would have to be able to swim great distances and still have the strength and stamina to carry out their mission and still escape unharmed.

They would need specialized breathing equipment that would allow them to breathe underwater. In order for the apparatus to allow for long range penetration of enemy held areas, it had to reuse the exhaled breath of the diver while preventing exhaust bubbles from escaping and giving away the position of the diver. It had to offer extended time underwater, be light weight, versatile and dependable. It had to be a rebreather.

On the morning of June 6, 1944, Operation Overlord commenced. It was an event like none other and was divided into many parts, each of which had to work with the others to be successful. It was also the beginning of Operation Neptune and began the invasion of France at Normandy. It was D-Day. It was the largest amphibious invasion in world history.

Those landing from water were to land on one of five beaches code named Utah, Omaha, Gold, Juno and Sword. The hard thing about such an invasion is that it is hard to hide. When those occupying the land do not wish to be invaded, they resist.

Fortifications, hedgehogs, steel and concrete spikes, some steel tetrahedral, mines and other hazards had been placed on the beaches and in the water. Guns were placed on heavily fortified bunkers perched on the hillsides. Fortified machine gun nests had overlapping fields of fire. And the guns of Pointe Du Hoc could rain down hell on both Utah and Omaha beaches and sink vessels at sea 15 miles out.

Before the landing craft could land the fortifications blocking their way had to be destroyed. Naval demolition teams were responsible for those obstacles underwater and the Army engineers above water. But plans never quite work out the way they are supposed to.

The weather changed. Conditions worsened but once started Operation Overlord could not stop. The degrading weather cost them time and high tide was missed. Because the tide was out when the demolition teams made it to their objectives, most of the obstacles were out of the water. The naval group took those seaward while the army teams placed explosives on those closer to land. On D-Day, they were not all referred to as frogmen. Those from the Royal Navy were Landing Craft Obstruction Clearance Units. More commonly called Lockyews.

LCOC

photo credit: www.wikipedia.org

Landing Craft Obstruction Clearance Units
The ‘LCOCUs’ were a vital part of the D-Day invasion forces in Normandy. Four Royal Navy and six Royal Marines units comprising 120 divers wore newly developed neoprene suits with ‘blast proof’ kapok jackets underneath, helmets, breathing apparatus and fins.They laid the foundations for the Very Shallow Water (VSW) and beach clearance techniques in use today.Those remaining after the war were eventually incorporated into the Clearance Diving Branch.

A RN demolitions team was working Gold beach. When they arrived, they found that the obstacles they were to clear were underwater. Each of the hedgehogs they were to clear had to have 36 small charges placed at strategic positions so that the steel would blow into pieces with none more than 18 inches above the bottom. Each of these obstacles was covered with pressure sensitive explosives designed to punch holes in water craft.

Lt. Hargreaves described the experience:

“We must have been about four hundred yards from the beach when the firing first started, and they didn’t forget to inform us that they knew we were coming. When we finally got on the beach we discovered that we were being systematically sniped, not only with rifles but also by odd bursts of machine-gun fire – a most unpleasant experience”.

On another beach one of the men described his experience like this:

“We were spotted from a tower ashore and were subjected to pretty heavy mortar fire during which a petty officer was killed and two men were wounded. Later the R.A.F. blotted out the tower and things were more comfortable although shells still kept coming over. One shell destroyed our breathing apparatus, which we had not been using as the tide was low. When the water came up later, Leading Seaman A. Robertson and myself tried staying underwater by holding our breath. We blew about fifteen obstacles in this way, but we couldn’t keep it up. We carried on the next morning, after sleeping in a R.A.F. crater, where incidentally we were subjected to fire from an 88mm gun.”

Dennis Shryock was 21 years old when he landed on Utah Beach. Dennis had been trained as an explosives specialist and one of those elite men who were the forerunners of our modern day Navy Seals.

The machinegun fire was deadly. They did not have the protection of being underwater and had to wade to each of the obstructions to place explosives. He said the water “looked like pure blood.” But they did the job.

According to navy statistics, at Utah, the demolition teams lost six men and had eleven wounded. Omaha beach did not fare as well. They lost thirty-one and another sixty were wounded.

the cliffs at Pointe du HocPointe Du Hoc
The water was rough from the stormy wind and the unexpected rain soaked equipment that was intended to remain dry. It took the landing craft longer to reach the beaches than expected. The plan was to hit the beaches at high tide; for the troops to be able to take shelter in the bomb craters as they made their way up the beaches. But they missed high tide. Most of the obstacles placed to keep the landing craft away were on dry land. When they were able to land, the troops had to run through wet sand 300 to 500 yards just to get to the bomb craters. Landing craft that had been fortified with bullet proof plating caused the crafts to ride much lower in the water. Too many of them were swamped and sunk before they could reach shore. The majority of the soldiers on board, weighted by 70 pound of equipment, drowned. Those that survived had to face a wall of bullets and artillery shells. The guns at Pointe Du Hoc had to be taken. The 2nd Ranger Battalion had trained hard in preparation for this day. They had practiced climbing cliffs and had brought along firefighting ladders and rocket propelled grappling hooks to help make the 100 foot climb. But it had rained.The ropes were wet and the propellant used was calculated with dry rope. The ladders were hard to foot and difficult to climb. German machinegun fire was held to a minimum by sharpshooters on the ground but they could not stop them from dropping hand grenades in an effort to keep them from climbing. The 2nd Ranger Battalion clawed their way to the top using footholds in the mud and rocks and bayonets driven into the cliff side when necessary. It took them twenty minutes to make the climb and take the Pointe. They held it for two more days before reinforcements reached them. Of the 200 men that started, only 90 were left in fighting condition.

What exactly was the breathing apparatus used by the USN frogmen and the Royal Navy Landing Craft Obstruction Clearance Units? It was able to supply an extended amount of breathing gas underwater by reusing the exhaled breathe of the diver. It did not allow exhaust bubbles to escape and was stealthy. It was lightweight and maneuverable. It was a rebreather.

While only remotely similar to rebreather units today, the ones used in 1944 were many generations of development old. In fact, the Italians started the concept of underwater assault teams using specialized equipment. And they recognized the need as early as World War 1.

In 1918 two members of the Regia Marina (Royal Navy) literally rode a torpedo into a harbor and sank an enemy ship. At the time, they had no breathing equipment and had to guide the torpedo at the surface in order to breath. They sank the ship but were captured when they tried to swim away. These human torpedoes became more like mini submarines and were human guided. Obviously the ability to be under the water, able to breath and stay stealthy was an advantage.

By 1941 the Italian navy had both a surface unit that operated fast, explosive motor boats and a subsurface unit that used manned torpedoes. Within this group they also had assault swimmers. It did not take long before other countries developed their own versions.

The idea of an underwater warrior is older than modern history. The functional ability to use such a warrior has always been limited by the inability to breath underwater. Throughout history, man has found ways to extend his time underwater and by the turn of the 20th century, some of the first closed circuit rebreather systems had been experimented with and used. The rebreather units used on D-Day were rudimentary compared to the modern versions we see today. But at the time, they did the job and those who used them had to be beyond courageous.

On June 6, 1944 those underwater warriors had a mission to do and short of being killed or captured, that is what they did.


Mark PhillipsMark Phillips is a retired 33 year career firefighter and Public Safety Diver; A Master Scuba Instructor an ERDI trainer, and Publisher of PSDiver Monthly, an Internet magazine dedicated to advancing the safety and knowledge of the Underwater Investigator.

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!

Don’t Trust Your Gas Blender – Analyze Every Tank

by Jon Kieren

Analyzing your tank

Photo Courtesy of Andy Phillips

People make mistakes, it’s human nature. I make them all the time. I’m sure that even after this article has been edited several times and published someone out there will find at least a couple of typos and call us out on it. A typo is one thing. However, a simple mistake in the blending process can result in a diver breathing a mix with significantly more or less oxygen than they had expected, causing serious injury or death. If we KNOW that people make simple mistakes so often, then why do so many nitrox divers today NOT analyze their gas before diving? There are two primary reasons: either they don’t understand why it’s so important (a topic that is covered in every nitrox course), or they have just become complacent. This article will discuss both scenarios and how to avoid them.

Why is it so important to analyze your breathing gas? Simply, it can kill you if it’s wrong. If the oxygen content is less than the diver had expected, they can end up with unexpected and unknown decompression obligations.

Example – You make a dive to 30 metres/100 feet assuming you’re breathing 32% nitrox. You spend 39 minutes on the bottom and surface with no decompression obligation. Unfortunately, the nitrox tank you were diving was accidentally filled with air (21% oxygen), and in reality you just blew off 26 minutes of decompression. A significant error that is almost sure to result in Decompression Sickness. This situation can be made significantly worse by conducting repeated dives.

What if the oxygen content is HIGHER than you expected? Should be better off then, right? As far as decompression obligations are concerned, yes. However, a far greater risk in diving nitrox is Oxygen Toxicity and can cause severe convulsions (not a good situation underwater).

Example – Using the same dive as above, assuming you were on 32% nitrox at 30 metres/100 feet, your partial pressure of oxygen (PO2) would be close to its upper limit at about 1.3 ata. If that nitrox mix was in fact a 50% nitrox mix, your PO2 would now be over 2.0 ata and would be considered extremely dangerous.

The examples above are not the only concerns of breathing the wrong gas at the wrong depth; a thorough nitrox course will cover the others, as well as how to avoid them. So if you have to be Nitrox certified to dive nitrox, and the risks and proper procedures for avoiding those risks are covered in the course, why do people still end up breathing the wrong gas? The simple answer is: complacency. Over time, divers become complacent with their gas analysis procedures and start to skip it altogether, which means they end up in the water with absolutely no idea what they are breathing. Pretty scary.

Normalization of deviance is a term used by astronaut Mike Mullane (*Mullane 2014) to describe the process of complacency in safety procedures. In brief, it explains how humans have the tendency to take shortcuts due to different factors including time, peer pressure, etc. Once this shortcut is taken and nothing bad happens, the brain will incorrectly assume that the shortcut is “safe”. This shortcut now becomes the norm, and we have completely eliminated a critical step in a procedure. This applies to diving at every level. How many times have you seen divers jump in the water without doing a proper predive check? It is taught and its importance stressed in every open water course, yet it gets skipped every day because so many divers have “gotten away with it” they assume it’s safe to dive without making predive checks and then eliminate it from their procedure. Unfortunately, it also results in emergencies from divers forgetting to turn on their air and inflate their BCDs.

The same happens to nitrox divers. Maybe one day they are in a rush and forget to analyze their gas at the fill station. They get to the dive site and realize that they forgot to analyze but now do not have access to an analyzer. They are left with two choices, either not dive today or dive without analyzing their gas. The diver has been getting fills from that fill station for years and has never gotten the wrong mix, so they decide to dive anyway and assume the fill is correct. Nothing bad happens, so they now believe this shortcut is safe. “If I get my fills from XZY Dive Center, I know that it will be correct and I do not need to analyze my gas”. They have eliminated the most critical step in diving nitrox, and this is now the norm.

We know people make mistakes, and that’s why we have safety procedures in diving. These procedures help us catch the little mistakes before they create catastrophic emergencies. When diving nitrox, analyze every tank before every dive without exception. It could save your life.

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* Mullane, Mike. (March 2014). Stopping Normalization of Deviance.

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
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Traveling With a Rebreather

rebreaterstuff
With airlines tightening luggage restrictions, packing for a dive trip is hard enough with just recreational gear and traveling with a rebreather adds another level of difficulty. What to bring, how to pack it, will the dive center have everything I need when I get there? These are all questions that need to be addressed, but if you tackle them one at a time, you’ll realize traveling with a rebreather can be very simple.

“What should I bring?” This question goes hand in hand with “will the dive center have what I need when I get there?” The first step in determining what to bring on the plane with you should be finding out what the dive center has available. Most dive destinations around the globe now have at least one or two “rebreather friendly” dive shops. It’s very important, however, to call and verify that they can accommodate you. Do they have the correct cylinders for you? Do they stock sorb? Do they have bailout cylinders available? Do they have high pressure O2, and can they blend the diluent you need? It is very crucial to ask these specific questions, as many dive centers advertise themselves as “rebreather friendly,” but in reality are just “rebreather tolerant.” Once you know for sure what the dive center is able to provide, the next step is figuring out what you need to bring. If you are traveling to a remote destination, you may experience a bit of sticker shock when you see what they will charge for sorb and cylinder rental. It’s important to remember that many remote locations (especially islands) incur huge shipping charges and import taxes, and these costs are often passed on to the end user. It may seem cheaper to bring your own cylinders and sorb, but this typically ends up being more hassle than it’s worth. We recommend traveling light and supporting the local dive center by renting/buying from them.

“How do I make all THIS fit in THERE?” It can seem like a daunting task when all your dive gear is laid out in front of you, and you have only a few small bags to fit it in. However, there are a few tricks to helping you get everything you need to where it needs to go safely. Try to carry on as many of the critical components as possible. Things like the head, canister, loop, counter lungs, mouthpiece/BOV, regulators, and electronics can easily be damaged/lost in checked luggage and leave your unit inoperable, so it is best to carry them on. Things like wings, harnesses, fins, masks and exposure suits are pretty resilient to rough baggage handlers and can usually be rented at your destination if they go missing. If you must bring cylinders and sorb with you, it is typically best to check them. Just be sure to include a Material Data Safety Sheet with the sorb and remove the valves from your cylinders. You are required to leave the cylinder openings unobstructed so they are easily inspected; agents have been known to simply confiscate/dispose of cylinders when this rule is ignored. It is always a good idea to photograph everything as it is being packed, this way you have evidence if something is lost or damaged by the airline. The fee for an extra bag is typically less than for an overweight bag, so it’s not a bad idea to bring along a small mesh dive bag that you can pull out and transfer gear into if you end up overweight at the ticket counter.

So everything is packed up, you’re at the airport, bags checked, and you’re going through the TSA checkpoint. As long as you remembered to remove any tools or knives from your carryon, things should go pretty smoothly. It can be fun to watch the look on the TSA agents face as your bag goes through the scanner, but after a quick inspection there usually is not an issue. Remember, they are just doing their jobs, and a rebreather head and scrubber canister looks pretty suspicious on an x-ray. We have found many TSA agents are now recognizing rebreathers, especially in popular hubs to dive destinations. Just assume that your bag will be inspected and plan a few extra minutes to allow for this.

So you know you’ve brought everything you need to enjoy a great holiday with your rebreather and all your critical rebreather components have made it onto the flight with you. Now it’s time to sit back, relax, enjoy the flight, and have a great trip.

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

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