Deco in caves

[Johanan]

How does one plan and perform decompression in a cave, if the physical ceiling does not permit to follow planner's/computer's instructions?

 

[tursiops]

I assume you mean that the computer says to stop at (say) 20 ft for 5 minutes, but you are deeper than that?
You just keep exiting until you get to 20 ft, by which time your computer may not even ask you to do the stop.

It is nice to have a computer like the Petrel that is much more relaxed about your stops, and will pretty much adjust to what you are doing.

 

[matt_w]

How does one plan and perform decompression in a cave, if the physical ceiling does not permit to follow computer's instructions?

Deco is covered pretty well in most full cave courses. Having said that, part of awareness in gas management should include planning to do a stop twice if there is a significant ascent in the middle of the dive. If you think about it, the situation you describe would not ever happen. If you can't go up from your current depth, you are not in need of a stop.

Like cave diving in general, deco cave dives require training and experience to do properly and safely. Training and experience are the only things that will help you make the decision to go back down mid-dive.

 

[Johanan]

Perhaps I should wait until I come to the Full Cave course...:blinking:

 

[tbone1004]

what they said, but confused about what you were actually asking. If you're asking how you plan decompression in a cave, it's very difficult to do it on paper because you don't always know what the exact depth profiles are going to be, i.e. no cave dives are square profiles. That said, there are many ways to approximate, but it is significantly easier to know roughly what your obligations are going to be and follow your computer for the exact numbers. As far as depth is concerned, you head out to where you need to be for the right depth. If you're stuck in a chimney, you have to stay there. It's annoying especially in high flow caves, but necessary evil.

 

[Scubadude_LA]

I prefer progressive penetrations into a new site. Not taking anyone's word for the lay of the land. I like taking the time to specifically document time/depth at major waypoints. Then plan a profile that uses known time/depth waypoints that I created. Basically like any tech/deco dive. Plan the dive on paper, then run the computer to verify that you are on schedule/ I would not do educated guess planning on a 300' dive on trimix and plan to ride the computer out. Aside from deco, gas supply is a real big concern that the computer can't help you with.

 

[karstdvr]

How does one plan and perform decompression in a cave, if the physical ceiling does not permit to follow planner's/computer's instructions?

Good question. The best thing is ask people that have prior experience and learn what is SOP for that system. For example, I can think of a place where there is a tight restriction at 20ft that allows two people to sit at 20',but if there is a 3rd person, they are going to have to plan for 30', and perhaps use EAN80. Another place the deco in lake water during the winter can be horrible due to it being in low 40', so you deco on EAN 60 to be able to sit in the spring water,which is much warmer.

 

[boulderjohn]

What several people have said in essence is you need to have a pretty good idea ahead of time what the cave is going to be like and what sort of conditions you will encounter both in terms of time and depth of the dive and the shape of your exit. Then you have to make some common sense decisions about what you need to do. You fine tune it according to what you actually encounter.

Let's say you are doing a deep cave like Eagle's Nest. You should know the maximum depth you will encounter, you should know roughly when and how you will turn, and you should therefore have a pretty good idea when you will get to the ascent line and what your deco obligation will be at that point. You should know you will be doing some of the deco in a chimney that restricts the number of divers in it at the same time, and you should know you will be doing the final stops in a basin with room to spread out. All of that should give you a pretty good idea of your deco plan before you get there. Your computer may give you something a bit different, but it's not going to be wildly different, assuming you followed your plan.

 

[uncfnp]

What several people have said in essence is you need to have a pretty good idea ahead of time what the cave is going to be like and what sort of conditions you will encounter both in terms of time and depth of the dive and the shape of your exit. Then you have to make some common sense decisions about what you need to do. You fine tune it according to what you actually encounter.

Let's say you are doing a deep cave like Eagle's Nest. You should know the maximum depth you will encounter, you should know roughly when and how you will turn, and you should therefore have a pretty good idea when you will get to the ascent line and what your deco obligation will be at that point. You should know you will be doing some of the deco in a chimney that restricts the number of divers in it at the same time, and you should know you will be doing the final stops in a basin with room to spread out. All of that should give you a pretty good idea of your deco plan before you get there. Your computer may give you something a bit different, but it's not going to be wildly different, assuming you followed your plan.

When I started cave I wondered how you would plan deco dives given the obvious limitations. I think this is the clearest explanation I have seen.

 

[Capt Jim Wyatt]

Perhaps I should wait until I come to the Full Cave course...:blinking:

Excellent advice!!