More than "Advanced", but not really "Technical"

[maniago]

If you want to learn how to do emergency light deco on a single tank with no redundancy.... what is there to learn? Read the computer manual, practice stops, learn to manage your air consumption calculations... None of this requires any real training, just read the book... of course you do need to know how to do a safety stop.. and what value is the certification, if you plan on never using it except in an emergency.

Heck you can even do a "safe" simulation, use nitrox and punch in air and then put the computer into a little light deco... and have a back up computer running your actual mix of nitrox..

I'm interested in this same area of understanding as the OP. That said, reading the computer manual doesnt hack it for me - if my computer goes deco, it basically aborts the dive and tells me to go to 10' and wait there for some specific time, completely ignoring what depth I'm at. It doesn't help me understand what is going on, just "gets me outta here".

Before I go to a PADI40 or GUE Fundies course, I'd like some written education about what deco procedures entails and be walked through a simulation or something - I don't want to enroll and then discover its not for me.

Where does one go to read the book knowledge?

 

[doctormike]

OK, now I see what Lowviz was saying... Yes, I think that it's a good idea for every diver to understand the implications of inadvertently incurring a small deco obligation (defined as one that can be completed with the existing backgas only). This would primarily be of use to people with good SAC rates but poor situational awareness.

It would seem, however, that if you weren't giving a course that actually taught deco procedures and planning of staged decompression, the best you could tell these divers would be "if you computer says you have a deco obligation, then just do what your computer says and don't ascend / surface until you have made it happy". Yes, that's a terrible approach for someone actually planning a dive requiring this type of decompression, but that's not what the target audience is. And including enough material in the course so that these divers actually do understand deco theory, and do know what to do if they have a deco obligation but then their computer fails (ratio deco?), would probably push them over into one of the basic tech courses.

But I agree with Lowviz that it's not a bad idea for OW students to understand what it means if they go past NDLs, so that they don't panic and think that the best thing to do is to exit the water right away even though they have plenty of gas left...

---------- Post added January 6th, 2014 at 09:33 AM ----------

I can't get into specifics, but extending downtime is not an option. It is all about safer ascents. I would much rather see her plan for and go into light deco on backgas than fudge her diveplan/computer to get a longer dive.

"I can do XX bottom-time with this computer, but only XX bottom-time with that computer". It's ludicrous IMHO. Your body dictates what you can and cannot do without getting bent. Nothing changes in that reality, regardless of what is strapped on your wrist.

Devon says it best. Your DCS risk is your DCS risk, and swapping computers doesn't change that. I took a chamber ride myself while staying far away from my NDL limits - if you dive, you risk DCS. But there are things that you can do to minimize that risk.

Now if you want her to plan to go into deco, then she shouldn't cut corners and she should take one of the courses recommended here. But that's different from what your other point was about inadvertent deco obligations...

 

[lowviz]

...//... Now if you want her to plan to go into deco, then she shouldn't cut corners and she should take one of the courses recommended here. But that's different from what your other point was about inadvertent deco obligations...

Yeah, there was some "thinking out loud" going on here...

 

[tursiops]

if my computer goes deco, it basically aborts the dive and tells me to go to 10' and wait there for some specific time, completely ignoring what depth I'm at.

I doubt this is true. For "light" deco, having overshot the NDL just a small amount, it may turn out that way....go to 10 feet and wait a specified time, and in fact the depth you are at is indeed irrelevant. But as the deco obligation grows, the 10-foot stop grows, and then a shorter 20-foot stop is added in, and later a 30-foot stop.

What computer are you using?

 

[maniago]

I doubt this is true. For "light" deco, having overshot the NDL just a small amount, it may turn out that way....go to 10 feet and wait a specified time, and in fact the depth you are at is indeed irrelevant. But as the deco obligation grows, the 10-foot stop grows, and then a shorter 20-foot stop is added in, and later a 30-foot stop.

What computer are you using?

Well it is infact what happened to me when I forgot to enter my EANX and dove it as air instead. Yeah, I can ignore it and pop back up to some depth greater than 10' and wait for it to clear, but clearly that's flying blind, not knowing how severe an infraction I've caused. I'm diving an Oceanic VT4.

 

[victorzamora]

maniago, I dive a DG03....which is the computer the VT4 is based on (read: practically identical) and that's not at all how it works. You must be misreading your computer. Computers WILL follow deco procedures. When I go into deco on mine, it tells me I have a ceiling at 10ft. As long as I stay below the surface, it's keeping track of my ongassing/offgassing (well, theoretical on/off-gassing). As long as I stay below that ceiling, it considers me safe. My computer automagically keeps track of it all, and adds a 3min SS on top of all deco obligations. I'm sure yours does the same.

As far as where to get the books for some light self-study, most dive shops will have them. Tao of Diving, Diving Encyclopedia, and AN/DP books are good initial reads. Also, I'm PMing you about other books.

 

[doctormike]

Well it is infact what happened to me when I forgot to enter my EANX and dove it as air instead. Yeah, I can ignore it and pop back up to some depth greater than 10' and wait for it to clear, but clearly that's flying blind, not knowing how severe an infraction I've caused. I'm diving an Oceanic VT4.

I don't understand why you think that you are flying blind - you were diving air (as far as the computer knows), you went past your NDLs, and now you have a deco obligation. So your computer says based on your current nitrogen loading, you would need to ascend and start your first staged deco stop at 10 feet. Of course, the computer can't make you ascend, so if you continue your dive, and continue your nitrogen loading, it will assign you successively more deco, as tursiops pointed out.

If you want to plan a deco dive, then there are computers which will give you more information (e.g. tissue compartment loading graphs, like my Petrel), but that doesn't change the fact that your computer thinks that you will be bent if you do a direct ascent, even though you think you are safe because you know something that the computer doesn't (your EAN mix).

But doesn't the VT4 let you do gas switching? Maybe that would help in this particular situation... I don't know that computer...

 

[rhwestfall]

liking this discussion...... please keep it going

 

[maniago]

When I go into deco on mine, it tells me I have a ceiling at 10ft. As long as I stay below the surface, it's keeping track of my ongassing/offgassing (well, theoretical on/off-gassing). As long as I stay below that ceiling, it considers me safe. My computer automagically keeps track of it all, and adds a 3min SS on top of all deco obligations. I'm sure yours does the same.

Ah yes, that is right, a ceiling. My bad. That said, "ceilings" are not taught or even talked about unless you have some kind of deco class or deco-buddy to talk to etc, so my neophyte mistake is probably good to illustrate that just a little more understanding of how deco works would make those of us "rec-ies" a whole lot more "aware" of what it means and how to be safe, yes?

Thanks on the books.

 

[ianr33]

if my computer goes deco, it basically aborts the dive and tells me to go to 10' and wait there for some specific time, completely ignoring what depth I'm at.

That's not actually what it's doing.

When it first goes into deco it will require a 10 foot stop,but it's not aborting the dive.Just telling you how much deco is required at that time.
If you stay longer at depth the time required at 10 feet will gradually lengthen and eventually it will require the first stop to be at 20 feet. Stay longer and you will see a 30 foot stop and so on.

Doing significant deco on some (most??) recreational computers is not a good idea. My old Aeris computer indicates the length of time required at a particular stop. e.g after a long/deep dive it might say 3 minutes at 30 feet. What it does not tell me is that the total time to surface (30,20 and 10 foot stops) might be 40 minutes. In that situation I would have no idea how much deco I need to do,or if I have enough gas to do it ! Not a good situation.

The other problem is the algorithm may not be the best. When my Aeris is asking for the first stop at 30 feet my Shearwater probably wants the initial stop to be at 80 feet (Depends on depth/time obviously,but it's MUCH deeper. )