How to master the complexities of extensive explorations of underwater caves and other overhead environments. Distance of 700 meters from the entrance to the end point. The depth of 164 meters at the beginning of the actual exploration and 186 meters at the end. Duration of the dive, which including deco stops, required a run time 9 hours and 46 minutes submersed.
Our case story will be a recent actual exploration where the dive profile posed a few challenges:
- Distance of 700 meters from the entrance to the end point
- The depth of 164 meters at the beginning of the actual exploration and 186 meters at the end
- Duration of the dive, which including deco stops, required a run time 9 hours and 46 minutes submersed.
However, even if this specific dive profile presented us with some exceptional challenges, it wasn’t fundamentally different from other technical dives in terms of safety and logistic considerations. We do our preparations and make plans in which we try to reduce the number of unknown factors as much as possible.
In technical diving “what if...” and “plan your dive and dive your plan” are all basic mantras. It is only the magnitude of the undertaking that changes as well as the levels of complexity. Even for a practiced tech diver, who routinely dives his twin 12-liters tanks and uses ready made tables, dives like this are much more complicated.
1. Defining objectives and means.
In this case, the objective was to explore an underwater cave that would take divers beyond the depth of 164 meters before they made it to the end. In this case, we planned as if we were diving to a depth of 200 meters and ranging more than 700 meters from the entrance. On the actual dive date, we may then find that these preset definitions of depth and time do not match up with the actual diving profile, mental and physical fitness, and the equipment at hand.
This leads to postponements and delays, which may run into a year, or at least several months of waiting, which is often the case. It is thus necessary to stay fit and keep practicing all the relevant technical skills. In this case, I kept up a regular schedule doing many speleological/cave dives where I could rehearse practice stage and travel procedures as often as possible, as well as practicing deep and rebreather dive profiles.
In the beginning of May, we found ourselves in Egypt. After one week of diving between 50 and 100 meters deep with stage and trimix, I had also made five dives to depths between 65 and 180 meters on rebreather in order to build some routine with real deep dive profiles and to test the 150 meter barrier.
Physical fitness training was not an issue, as I practice every year around 4-5 times a week by running, swimming and bicycling, so I simply took a nice break the week before the actual dive.
Knowing the location
This cave is quite the labyrinth and has several levels. So, it is a good thing I knew it rather well. A year ago, I first dived it to a depth of 60 to 90 meters before going down to 150 meters. And the week before the dive, I had returned with a rebreather, going to the 70-meter mark, just to memorize the route, using a scooter, to avoid wasting time when we were going to do our exploration.
Needless to say, I had also gone over the available topographic information and reports from previous dives in order to get a clearer picture of equipment load during the dive, restricted passages, currents (what if it rains the preceeding days?),visibility and necessary permits. In nature, it is not any different from when you check the weather forecast, prevailing currents and swell before you go on a dive in the ocean.
2. Choice of equipment
The choice of gear must reflect the depths and environmental hazards. For example, when I did my 330-meter dive, it was obvious to go with an open circuit system, since I had never been beyond 150m on a rebreather. And no one has ever gone deeper than 270 meters on a closed circuit rebreather.
On the other hand, the closed circuit system (or semi-closed circuit) is the latest trend amid serious underground exploration dives for a number of good reasons: - greater autonomy - greater gas economy - breathing a much less colder gas - less tanks to manage Possibility for using helium—in the form of heliox—for the entire dive, significantly improving the decompression profiles.
My Voyager dive computer has a battery life of at least seven hours, making it possible to complete the entire dive, starting from the entrance until the bell-area. My other technical option was to stick with the usual open circuit system with complete redundancy.
We had to bring a few 20-liter tanks inside the cave, between the depth of 110 meters, which was 600 meters inside the cave, and the dive bell at 12 meters. It was a bit heavy, but in case of a complete failure of the closed circuit, it would have allowed me to make it back to the bell area from the deep end. This also permitted the team to familiarize themselves with the cave.
The scooter or, as it is appropriately termed, the Diver Propulsion Vehicle, was also a requirement because of the distance to be traveled. Several trips starting from the deep end, which was 500 meters from the entrance, helped me to select a model that can really tow, rather than a lighter one. The former, although a little less speedy, seemed to me to be more maneuverable inside that particular cave.
The deco stations The possibility of mounting a deco station was extensively used. The choice was between a mobile deco station—suspended between 11 ...