CCR Cave Training

January 2007

So how do you read a cenote? Well first you look at where the leaves and twigs that have fallen in the water collect. That is the siphon side. The clear end of the cenote will be the spring. Then look for the "inky darkness" and that is where you want to go. Many caves in Mexico are very light limestone so the bottoms of cenotes can be quite white in colour, except where the cave starts. The black hole that is the cave beckons us to enter and we can't wait to answer the call.

Ron, Mike and I have just started what we will soon discover is the most challenging dive class any of us have ever taken, Closed circuit rebreather full cave diver. If cave diving is considered the most extreme form of recreational scuba diving then our instructor, Matt is one of the most extreme cave divers in the world. He has logged over 2500 cave dives throughout the world and was safety diver for many cave video projects including the feature film "The Cave". His name also appears on many cave maps throughout the Mayan Riviera as an explorer mapping new tunnels and cave systems. We were fortunate enough to have Matt share his vast knowledge with us over the next 7 days.

Our first challenge, other than getting to class on time was to do a circuit on a cave line in open water with our eyes closed. "If you open your eyes I will rip your mask off" Matt warned. "If I catch you doing it again I will assume you are afraid of the dark and we should discuss if you should be here". We swam around the cenote, while making contact with the guideline with our eyes closed. All the while Matt is attempting to entangle us with anything we have dangling, and at one point pulled the guideline from my fingers. Fortunately I remembered my training from my intro cave course one year previous and used my safety reel, made a tie off and did a proper lost line search. This must have endeared me to the instructor since he seemed to leave me alone for the rest of the dive. Our next dive was into the cavern zone. Dark enough to require lights but still close enough to the exit to see some light coming through. Since we were diving with rebreathers we found our open water bouyancy habits to be a little wanting in the cave where bouyancy is ever so important. Those of us who let our fins touch the cave floor soon felt the sting of Matt's dive light rapping our ankles.
The caves in Mexico are beautifully decorated with stalactites, stalagmites and many other formations (known as speliothems) due to the fact that as recently as the last ice age (around 12,000 years ago) these caves were dry and limestone bearing water dripped from the cave ceiling making the glorious formations we see today. These delicate limestone formations take thousands of years to form. It only takes one misplaced fin or one scraped tank (or rebreather cannister) to damage these formations forever.

One of the main benefits of diving rebreather in a cave is the much longer run times. When diving with open circuit scuba your time is limited, you have just so much air to get from A to B and back, leaving some for emergencies. With rebreather cave diving time is much less the enemy. Our main limitation was bailout gas supply. Bailout is the emergency open circuit scuba we carry in the event we have a failure of the rebreather. For the first couple of dives we carried 40 cubic foot tanks slung on our left side for bailout, and we soon got used to using it. On our third dive we had to simulate a failed rebreather, and light. We switched to open circuit bailout and turned on our backup lights and began exiting the cave. I was the last man in the group and als I started to lag behind found myself getting further and further away from the other members of the team. As they pulled away from me Matt came out of the gloom and signaled to me to stop swimming to see if my team-mates would come back for me. It was soon apparent that they were going to leave me so I was told to start swimming for the exit. Matt signaled a second time for me to stop. He wanted to drive a point home to my team-mates by delaying my exit so they could see how far behind a team member could get. Unfortunately my delayed exit was causing my breathing rate to speed up a little bit and shortly after Matt signaled me to start up again I noticed my reg was not breathing as well as it should. I could see the cave exit as my second breathe came through a little harder. I quickly realized that my tank was nearly empty and although I was aware that my rebreather actually did work when my reg finally failed to deliver life giving air I got the chilling thought of what it must have been like for the 400 or so divers who have perished in caves over the years when that same hard breathing sensation came over them. This was just an excercise but it was a sobering realization that things can go bad really fast in a cave. After that dive we decided to all carry larger bailout cylinders so 80cubic foot tanks were clipped on for the next dives.

Our agreed upon bailout range was to be 1500 ft penetration with these larger tanks. It is usually considered that 50 feet per minute is a good pace for cave diving so although we had many hours of bottom time our range was limited by our bailout to be within 30 minutes from the cave exit. That was all well and good until we did our first eyes closed touch contact exit from the cave. It was here we discovered that 50ft per minute is fine when you can see but in the dark you can expect to take at least twice as long to exit. Now we had to decide whether to carry more bailout gas, limit our cave pentration or adopt a different approach to bailout called team bailout where we agree to share bailout gas in the event of any team member having a failure. This seemed like a great idea until we had to practice it in total darkness.

For our next dive we decided as a team that should there be a rebreather failure (and we were pretty sure one would happen) that the affected team member would take up the middle position so that they could access either of the other members bailout gas. Looked good on paper I guess. I was team member 3 so I was last in and therefore first out. When the lights when out from a signal from Matt, I soon got the tap on the head and the signal indicating I would be "it". I switched to my bailout in the total darkness and signalled by touch to the next member of the team I was on bailout and he was to switch positions with me. I moved hand over hand to the next position in line and waited patiently for the last man to make touch contact by grasping my elbow so we could start our exit. I waited for what seemed like an eternity then started moving away from the exit toward where the last man in line should have been in contact with the guidline. I soon realized he wasn't there. I turned toward the exit and began making my exit as a solo diver, on bailout, in the dark.... I soon got a tap on the head from Matt he had me watch as my two other team-mates were making a touch contact exit blissfully unaware that I was not among them. They both looked rather sheepish when I finally emerged but it was decided that switching positions when in total darkness was not a very good idea. Matt had driven home the point quite well.

One of our dives involved crawling over a bedding plane, which is a low ceiling very wide tunnel where the only way to get through is crawl on your belly like a reptile. This was over very jagged limestone known as velcro rock for obvious reasons. Even though our rebreathers and tanks clanked and banged as we shuffled through Matt effortlessly glided through like a ghost; and he is not a small guy. We soon came to a landmark that indicated a jump to a rarely used line leading to a beautifully decorated room. This was to be our turn around point but it was great to have a dive where we could focus on the cave on not skills and drills. We were finally starting to feel like cave divers instead of marine recruits.

Much planning and preparation went into taking this course in Mexico and packing equipment was a big part of that. One thing I wish I had not packed was a cold virus. Shortly after arriving the first sniffles showed up. I tried to ignore it but by day 3 things were getting bad. I went against everything I believe in and took medication before diving (gasp). Everyone seems to have a sure-fire remedy for a cold when you are sick but I first tried herbal remedies then by day 4 I brought out the big guns, Sudafed. It took me a while to clear my ears but I was able to do it so I kept diving.
One aspect of diving where rebreathers fall behind open circuit is up and down profiles. Prior to attending this course I considered myself to have pretty good buoyancy control. I can glide through a wreck, frog kicking merrily and usually not disturbing the silt too much. Wrecks tend to be fairly stable platforms with constant depths at least usually if you stay on one deck whereas caves can be very unpredictable depth-wise. Matt had taken us to Taj Mahal, a very beautiful cave near Akumal. It is also considered to be not rebreather friendly due to the roller coaster ups and downs we had to transit while diving this cave. At one part of our dive we came up from 50ft to about 6ft from the surface then back down to 50ft again. This was playing hell on my sinuses, never mind what it was doing to our buoyancy control. By the second dive my ears were killing me. I attempted to do it but had to give the thumbs up signal 20 minutes into the dive. After we headed back to Playa, Matt and I sat down to talk about my illness. We looked at IANTD standards and it seems I was just 10 minutes shy of meeting the minimum cave time to pass the course, I had thumbed the dive just 100ft shy of the true cave zone (we were still officially in the cavern zone at this point) so I needed one more cave dive of 10 minutes duration to complete this course.
So with my nose running like a freight train, my ears screaming with pain, I went back to my hotel room to decide if I want to quit now or finish the training. I woke up the next morning with every bone aching. Stuffed up and suffering from lack of sleep from the coughing fits I was having all night. I was going to call it quits but I decided to just put one foot in front of the other and see how far I got before it became unbearable. I assembled my rebreather as I did every day. Ate a light breakfast of eggs on tortillas and Sudafed and started packing my gear on Matt’s truck. We were heading to Tulum to a cenote called Escondido also known as Maya Blue. I was still feeling like crap but I was handling it OK so far.
When we got to the cenote I set things up and seemed to feel OK. I trudged down to the water with my gear and entered the cenote for a plan that called for 2 dives to complete a circuit. As I began my S-drill a stabbing pain in my left eye forced me to the surface. Matt pointed out that with a rebreather we have nothing but time to allow me to equalize my sinuses. I went to the stair in the cenote and one rung at a time made my way down to the bottom. The first dive was to set up then the second dive would allow us to make the circuit complete. It sounded like fun and I soon forgot about my ailments.
Unfortunately the team had miscounted the number of reels required for the execution of the plan so when it became apparent while in the cenote Matt was a little ticked and revised the plan to just do a cave tour instead with only one jump to navigate. This was to be a mostly relaxing dive. We had a couple of drills to perform but nothing too exciting then mostly enjoyed the beauty of the cave. After 74 minutes we came out had a quick debrief and I exited the water.
I was done (whew) and the other guys had one or two more skills to perform but I was off the hook and could give my aching ears and sinuses a rest. We drove to Tulum for a nice BBQ pollo and tortilla dinner then back to Playa for the course wrap up. None of us were entirely sure we had passed the course at this point so we had to wait like school kids waiting to see the principal while Matt interviewed us one by one. Mike, who did not have the benefit of previous cave training was probably the most worried about the final evaluation but in the end we all were given the nod and were now able to officially call ourselves cave divers.

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