As every good scuba diving instructor should do, I continually look for ways to improve my classes. Not just in presentation, knowledge, but also in safety. Over the past year, one of the things I have thought about changing in my technical diving class is how many bottles to introduce students to as well as what gasses to use for training. I consider myself an instructor who goes above and beyond course standards, but when it comes to this, you may be surprised.
First, I should let you know that for TDI’s Advanced Nitrox and Decompression Procedures classes, there is no maximum/minimum number of deco bottles that the students can train on nor is there a requirement as to what deco gasses to use. I have seen many technical diving instructors who will put two or three bottles on students at this level. The reasoning for some, is that it prepares the student for future trimix classes. I can see this. I do not believe that this is the direction that I want to take my technical diving students in.
I’ll Take One Deco Bottle, Please
When new technical diving students come into class, they have enough to worry about than trying to manage multiple deco bottles, especially at the Advanced Nitrox and Deco level. Certainly trimix classes are different. For this reason, I do not put my Advanced Nitrox and Deco students into multiple deco bottles. When learning technical diving, classes will be difficult enough. Trying to learn the new skills that come with technical diving and managing multiple deco bottles will just lead to the student not fully learning all of the skills.
When putting new tech students in only one deco bottle, they can fully master the skills of diving with one bottle before moving onto a second bottle. When adding a deco bottle, it adds another piece of equipment to be aware of. Every diver must have situational awareness of three things; their team, their environment, and their equipment. Adding the deco bottle when the tech student hasn’t fully mastered situational awareness increases stress. When adding multiple bottles to the same student, now the stress level increase significantly and their performance will suffer in the class. Allowing new technical divers time to adjust to diving with one bottle, they can use this time to increase the situational awareness for carrying that bottle. This way, when they move into a trimix class, adding the second bottle shouldn’t be that difficult for trimix students to learn.
The Advanced Nitrox and Deco class that I teach, I only teach with one bottle. I also teach to use a bottom stage to extend dive time and perform deco using back gas.
Real Deco Gasses, A Loaded Gun
Everyone knows that I follow the DIR mindset and use/teach standard deco gasses. However, during my classes, I do not allow my tech students to use real deco gasses. Instead, they use the same gas as in their back tanks (32% Nitrox). The exception is during the last two dives of the class, which are the experience dives where we do real decompression and use standard deco gasses.
By allowing students to carry real deco gasses, you might as well let them carry a loaded gun. The reason why I do this is simple. If a problem were to arise and the student were to be on a deco gas at the wrong depth, they could quickly tox. When doing simulated decompression, you could start the simulated deco shallower to lower the risk of dropping below the deco gas’s MOD. But if a situation were to come up or the students could not control their buoyancy, the risk for toxing is still greater than if on back gas.
By using back gas in the deco bottle, it lessens the stress that real deco gasses bring for tech students. When I was taking my technical diving classes, I remember the stress that having to stay right at the required stop depth. This stress caused me to increase my breathing and lose focus of my buddy. Heck, I remember draining an AL40 of 50% Nitrox when doing 12 minute simulated deco.
Summary
There may be plenty of reasons why tech instructors add multiple deco bottles and real deco gasses during their class. I, however, feel that less is more when it comes to selecting deco bottles and gasses for the Advanced Nitrox and Deco classes. By using back gas in the deco bottle, it greatly reduces risks when doing simulated decompression. Using only one deco bottle lessens student stress and will help increase their learning.
Dive Safe,
Duane Johnson
Precision Diving
Technorati Tags: technical diving, Nitrox
About Duane Johnson
This was the way I was taught, and I think the reasons for one bottle of backgas are cogent. It allows the student to play with the skills without being afraid of hurting themselves if they make mistakes, and that definitely lowers the stress. By the time you have a real deco gas in the bottle, you are solid enough not to worry about it any more than you should.
On my tech course (DSAT Tec Deep) we always trained with two deco bottles, but didn’t breathe from them until the last couple of dives. Both contained EAN50 though, so it would have been hard to make an error.