Category — Trimix diving

Deep Sinkhole photo shoot preparation Part IV (last part)– After unit modification of his AP Diving Evolution CCR Rebreather, Essential prep training and the ccr cave diver course it was time to take the training with my student Paul Nicklen to the next level and ad some Trimix into the equation in order to go deeper vertically into the caves.

Paul Nicklen at the Pit

As we go diving deeper the partial pressure of nitrogen as well as oxygen go up and become a serious threat to the deep diver in terms of nitrogen narcosis and oxygen toxicity. In order to control these to potential problems the non narcotic gas helium is introduced into the breathing mix. With a variety of formulas or software programs we can determine the partial pressure of oxygen we would like to have as well as the narcotic level we would like to have. Well … none please or not deeper than a 100 feet / 30 meter equivalent for me at least.

There is a variety of Trimix mixtures out there. Notably based on the oxygen content. If you see a Trimix label on a tank it has two numbers i.e. 30/30, 21/35, 14/55 or something similar. The first number is the oxygen content and the second number is the helium content. The balance is nitrogen. The MOD or maximum operational depth of a mix is directly connected to its oxygen content. If we have 30% oxygen in the mix our MOD as of partial pressure of oxygen with no more than 1.6 po2 (or 1.4 TOD target operational depth and working po2) is shallower then it is with 21% oxygen content and that 21% mix is shallower then a mix with 15% oxygen content. As less oxygen in the mix as deeper we can breathe it.

This first step of Trimix diving for Paul is based on Normoxic Trimix. Normoxic because the oxygen level in the mix is on a normal or 21% level as in the air that surrounds us. With the 21% oxygen content we have a MOD at 1.6 po2 of 218 feet / 66 meters.

As we started our training we had to go through some dive planning sessions to expand on the dive planning in terms of decompression stops and bailout gas considerations with hard calculator calculations and tables as well as software programs namely V-Planner. During the ccr cave diver course we have been concerned with mostly one bailout gas but in deep diving operations we have to keep in mind that in case the Rebreather is not functional at depth we still have an alternative path to the surface. Which introduces more bailout tanks into the equation as we need to decompress. In our case we choose to use Ean50 for o/c bailout decompression purposes alone.

As we calculated how much bailout gas we might need from depth all the way up we discussed team versus individual bailout gas strategies with its distinct advantages and disadvantages. As we choose our o/c bottom bailout gas to be a Normoxic Trimix 21/35 and our deco o/c bailout gas Ean50 we determined the volumes needed in order to come back up and with it tank size and amount requirements.

We started then to calculate out onboard diluent requirement which has the distinct need (in my opinion) to have a po2 of 1.0 at max depth. The reason for me is that if I need to make a drastic diluent flush I need to be able to see on my po2 that I am actually doing a successful diluent flush. Meaning if I am diving a 1.2 or 1.3 at the bottom and I do a aggressive diluent flush I need to see the numbers going down to 1.0 po2. That serves me well for sensor verification in case I need to determine which sensor to follow if they all walk out in different directions. In doing my calculations I will have a Trimix mixture in my onboard diluent tank that is not entirely Normoxic anymore. It is still above 16% oxygen content but not at 21% anymore. I am entering a zone where I can’t just breathe on any regulator or BOV anymore without thinking what is connected to it.

At this moment of our training our BOV’s are still connected to our inboard diluent tanks which serves as a step in-between to the large bailout tank which has all the volume to get us back to the surface. I do not consider that adequate and see the potential for sucking out the onboard diluent tank at depth before reaching the large bailout tank and see the need to change the configuration where the BOV accesses the large bottom gas bailout tank directly.

Before we do any deep dives it is back to confined water training to work with our bailout tanks along a cave line to sort out a number of issues including the identification, attaching and gas changes to the proper bailout gas in simulated zero visibility conditions. All went well and easy I have to say largely due to the fact that we just finished the ccr cave diver training program and Paul ze Nicklen was tuned up sharp.

As we started our Trimix deep cave diving we choose “the Pit” as our training grounds mainly due to easy access using the newly installed ladder and platform. We practiced free descends, descending down a line, free floating deco, decompressing on a down line and decompressing circling the walls of the large sinkhole called “ the Pit”. All went well and flawless including bailout ascents from depth into the shallows.

Paul Nicklen at the Pit

As we spend the days at “the Pit” I could not resist driving down memory lane.

The Pit 1997 Mike, Dan, Matt

When we did the exploration in 1997 with Mike Madden and Dan Lins being my dive partners (Dan and me found the BMB passage and Bypass Restriction), with Laura and Len Bucko “the bush pilot” our support divers we had to launch all our equipment on horses walk 45 minutes to Nohoch Nachich main entrance, then another 45 minutes to Far Point Station and then another 45 minutes to “the Pit” who has been found during a 5000 + feet exploration cave dive from the Dos Ojos main entrance by Kay Walten and Dan Lins in 1995 or 1996 I believe. Now you just drive right up to it. Clean parking. Gotta watch so you don’t actually drive right into it … would be a nice wreck dive though.

The Pit 1997

I had a great time spending 14 days diving with Paul ze Nicklen. He turned out to be a competent ccr deep cave diver and I have a lot of respect of what he is doing up in and under the ice, the images he squeezes into his camera.

The ccr unit modification, ccr essential prep program and ccr cave diver program where conducted out of ProTec Playa. The ccr Normoxic Trimix course was conducted out of ProTec Tulum.

Deep sinkhole photo shoot preparation Part III – After preparing the unit for horizontal trim and sorted out propulsion and rebreather emergency drills such as the three H’s (Hypercapnia, Hyperoxia, hypoxia) and the boom drill (internal and external uncontrolled gas release) we are ready for the ccr cave diver training program. It is only now that the student is actually ready to focus on the upcoming and cave specific training sessions.

The ccr cave diver training program is the most complex training program taught to students only topped by ccr Trimix cave diver programs. The complexicity is coming from the complex activity or rebreather diving combined with the complex activity of cave diving.

Before we jump in the water a long review of ccr dive planning practices is done plus the introduction of bailout range calculations including the optimization of bailout gases. The biggest difference between a oc cave diver and ccr cave diver are the bailout range or bailout umbrella. The ccr cave diver can spend quite a long time within bailout range (given he is within 1/3’s of sorb, o2 and diluent) diving down different lines to see a lot more cave then the oc cave diver who is bound to just go in and out of the cave.

The cave diver training program starts in the trees where we talking about laying a line into a cavern or cave, how tie offs are made, what the critical positions and tasks of each team member are. The student, in this case Paul Nicklen, learns how to lay a line and how to follow it in zero visibility feeling the line and tie offs. Touch contact communication is explained and practiced.

An introduction on what to do with the safety spool is given in case we have a lost diver or lost line in zero visibility situation. A full explanation of the drill including a full real time drill on land will be given later in the course before we actually do the drills inside the cave.

After the surface we move into a openwater area of a cenote with a large enough openwater pool. Most if not all Mexico cave diver students will know Cenote Eden or Ponderosa as it was called before. Many may know its nick name the pool of pain due to the pain felt by all students initiating their training here. The drill practiced on the surface are repeated in the openwater including a stress circuit where entanglements may happen in simulated zero visibility conditions. Once that is done to the satisfaction of the instructor we can move on into the cave.

The most difficult part of cave diving is to get from the openwater to the beginning of the permanently installed guideline due to the depth change and connected buoyancy changes that are more profound and difficult to deal with being on a ccr rebreather. Once we are on the permanent line and have tied in our reel we are free to cruise … until we do complex navigation in the form of T’s or jumps. The first day or two are spend with short penetration dives doing the three H’s drills, boom scenario, primary light failure and touch contact drills alone and as a team till survivability levels are reached.

Once the student is proficient in ccr and cave survival drills we move on to deeper penetration with constant and now un-briefed ccr emergency drills who now can and will happen at any time during any dive or situation to heighten the students awareness and hone emergency response time. During this period we go back into the trees on the surface to talk in detail about lost line in zero visibility and lost diver scenarios. Once the concept has been understood and drills have been mastered it is time to conduct the drills in the cave. I am of the opinion that the lost line drill is of utmost importance and must be completed successfully. If that can’t be achived on one dive we have the rest of the course to repeat the drill until mastered successfully and thus building confidence in the student.

As the student is getting more and more aware of its surrounding, developing better trim and propulsion, getting better with communication, has a good response to ccr related emergency drills and cave related emergency drills we move on to complex navigation in terms of T’s and jumps, circuits and traverses. A special lecture is given and back in the trees on the surface a spider web of lines is installed to explain hands on about how to do jumps, how to mark intersections and explain the communication within the team in order to ensure that every team member has seen and understood the jump or T that has been created and is now to be navigated. Failure to do so may have dire consequences when the team is coming out of the cave in a worst case scenario in zero viz, off loop and under high stress finding the intersection has not been marked properly. Marking properly means marking our very own exit to be easily identified under high stress and in zero viz..

Then we come to the heart of ccr cave diver training where we can penetrate the cave to maximum bailout range taking waypoint on the way in to mark jump off point when we are on the return leg of the dive towards the exit. As a ccr cave diver with sorb with 1/3, o2 within 1/3 and diluents within 1/3 we can jump off to side lines penetration to maximum bailout range and return to repeat at an different line closer to the exit. This way you can cover a very large cave area with multiple passages and jumps while staying within bailout range and consumable safe diving parameters. The complex caves of Mexico are extremely well suited for complex dives of this kind.

During these complex dives the repetition of un-briefed ccr related emergencies such as the three H’s and boom scenarios continues honing the students emergency response.

If the student would have entered the ccr cave diver training program without spending the time and effort of changing his AP Diving Evolution Rebreather into a highly efficient cave diving unit and would have not spend the time and effort in the prep program called Essential Diver program the student would not have been ready to receive, absorb and retain the information during the ccr cave diver training program as the struggle with the unit would have been to much.

The unit modification session and prep-program have been conducted out of ProTec Playa. When we moved on to ccr trimix cave diving we moved down to ProTec Tulum to be closer to the deep sinkholes and caves down there.

Stay tuned for Part IV – CCR Normoxic Trimix in the Cave