Cave Diving, Cave Exploration and Cave Mapping in Yucatan, Mexico
Caver Diver at Little Brother Cenote at Chac Mool Mexico

Risk of ICD and Narcosis When Bailing Out?

Great write-up Hans. Welcome back to NJ. Drop me a line and we can go out on my buddy’s dive boat some time. I’m heading to Florida in 3 weeks for CCR cave and CCR trimix training.
I have one question about your mixes. You didn’t say what you used, but doesn’t picking a lighter mix for bottom bailout put you at risk for ICD? Not to mention the narcosis causing a significant pucker factor.

To answer your question, the fraction of He only dropped by 10% when I switched from CC to OC.  That is not enough to create ICD friendly conditions.  A much larger change in the gradient is theorized to be necessary to promote ICD.  Consider this, if I were to go OC all the way to the surface the first gas change would have a 30% change in  the fraction of HE, the second would have another 30% change in HE content.  These changes do not throw an ICD warning in V-Planner (Which is arbitrary by Ross’ own admission.) and according to the principles I was taught in Trimix class should be ok.  So ICD isn’t a big concern here.

On the other hand, the Narcosis is a concern and that is one of the reasons I executed the drill.  I wanted to confirm I could still function under stress with that END.  The results of the test indicated that I was more impaired then I anticipated though not impaired enough to switch to a richer B/O gas for that depth and those conditions.

This provides a segue into another poignant topic; I never dove open circuit Trimix.  Therefore, I do not have any experience at depth on open circuit beyond bailing out.  This presented an interesting revelation to me; being at 280ft on OC is a fundamentally different experience then doing it on CC, which is something that Patrick Widmann warned me about more then once.

Watching my pressure gauge move noticeably with each breath adds a new sense of urgency and compounds the narcotic effect.  I now believe it is worthwhile to execute a number of OC Trimix dives to get a feel for gas consumption at 10ATA or more; if for no other reason then to learn the confidence and gain the experience to bail out in a calm and collected manner.

I can’t think of any worse set of conditions then to have to go off my unit, for a real emergency, and then to worry about my OC gas consumption and how it will play into my mental state.

I have tested and calculated my SAC rate many times, and it is very predictable.  However, knowing it intellectually and the pencil and paper jockeying wasn’t able to reproduce the feeling of watching the gauge fall.  It is one thing to know on the surface that your tank will be dry in 10 minutes; it is an entirely different feeling to experience it running down that quickly.  My experience is that the intellectual pursuit and mental preparation doesn’t substitute for experience and the only way to gain experience is to go out there and try it.  This is something Steve Bogaerts repeatedly hammered home for me and it was at his urging that Patrick and I both made the investment to execute these training dives.  Patrick had numerous sub-100M dives under his belt on open circuit, so his experience was different then mine.  I had no sub-65M dives on open circuit and I am new to Trimix diving, so I experienced something very different.  By both of our admissions, bailing out was a very beneficial, if costly, drill and was worthwhile.

I have observed the following; any uncertainty, doubt or fear will be magnified in an exponential way when the lizard brain appears on stage.   Therefore, it is advisable to train to mitigate as many of these primal fears as possible thereby freeing your mind to deal the real issue at hand with a “mind like water” focus.  Fear, doubt, and uncertainty cause me to react in disproportionate ways, causing more difficulty, inhibiting a calm collected solution.  The solution or at least the way to mitigate this is to train.

For example, NASA trains their astronauts for years prior to each mission.  This is to mitigate the response of the lizard brain and to ensure they have experienced, not read about, every possible contingency they can create here on earth prior to the mission.  This same approach needs to be taken into diving, especially as I reach further into inner space.  Deep diving with exotic gases in an overhead environment with relatively experimental technology is a highly risky endeavor.

The risk is so great because there is a disproportionately high probability that the unit will completely fail leading to death; known in gaming theory as ruin.  Therefore, with such a great threat to life possible on every dive, it is incumbent on the diver to train all the situations, including total system failure in situations as close to real life as possible..  Sometimes it is easy for me to assume I will react the right way, I had trained bailing out in 40ft, 100ft, and 240ft many times.  However, the training in 240ft only lasted a couple of minutes and didn’t involve a vigorous horizontal swim; which, upon reflection, presented a substantially different set of environmental, psychological and physical conditions.  It is important to realize that subtle changes in the situation can result in dramatic changes in the outcome and experience.  The threat is that we believe that a similar situation is applicable and overlook the fundamental changes in the environment.  A prime example is people assuming that experience and skill wreck diving will translate into cave diving and vice versa.  More then one diver has died making this false and fatal assumption.

What I learned was that when I move to the next section of cave which drops to 350ft (105m) and presents significant environmental challenges, I will want a richer HE gas.  I also learned that I want to train bailing out and perform an orderly exit in the conditions I expect to be diving in.  I think before I go for Jill’s Chamber, I had better be comfortable exiting from Wakulla Room on OC.

I hope that answers your question.