Decompression Diving

[DeepDiverBob]

Have you ever done a decompression dive?

[juls64]

I haven't had a need to yet, but I can see it in the future. There are a lot of wrecks in the Great Lakes (and other places) that interest me and I can see the need for further training down the road in order to get to them.


Julie

[M&P+4]

It almost seems like one more thing to try. I have countless other things ahead of it though.

[steve2281]

I did a North Carolina trip last year, and most every dive ended with a little deco. No, I'm not deco trained, but I had waited a long time to make that trip and wanted to get the most time out of every dive. Most everyone was diving some kind of high volume cylinder, so the choice was doing some deco or surfacing with 1800lbs of nitrox on your back.

Our operator did not condone deco diving, but instructed us to be one of the first in the water if we were planning on doing "extended safety stops." Even with nitrox, NDT get pretty short on back to back deep dives.

[Atlaua]

Well, there are really two questions here. Planned vs. Unplanned deco.

Actually, I've never done either. I'd like to do some real wreck diving in the future, not just the led trip through the C-53 but some of the GL and eastern coast wrecks. When I do I will take the necissary courses and plan my deco properly.

The other question is the unplanned stuff. You know you go down and oops, your comptuer says time to deco. I pay close enought attention that that hasn't happened yet. I've had my computer down to 0 minutes NDT but no ceiling. Last time that happened was at Devil's Throat. On my next Coz trip I plan to do Maricebo and I'm betting I will have a short deco obligation on my computer.

That being said if I were diving tables, a lot of my dives would have been deco dives.

James

P.S. Don't forget the cardinal rule....every dive is a decompression dive...

[Atlaua]

On a side note, I haven't answered the poll.

"No and you can't make me" doesn't apply, because I will when it's appropriate. Neither does "No, but I want to" because I don't have any desire to do deco just to do it. Some of the diving I want to do may require it but, the deco itself isn't a goal.

James

[theskull]

Well, there are really two questions here. Planned vs. Unplanned deco.

Actually, I've never done either. . . .

GOOD!!

Unplanned deco is about as wise as unplanned out-of-breathing-gas! There is no excuse for either. And PLANNED deco, if actually planned, will always include redundant first stages at the very least, and most likely a redundant gas source, not to mention having been trained in the proper procedures and theory. Why play with your life and health when you're out there to have fun? Is a few extra minutes of bottom time worth a few hours in a deco chamber and possible crippling disabilities?

Please dive safe all. Dive within your training and experience level.

theskull

[Atlaua]

You gotta ask, because I think more people do that unplanned thing than do that planned thing. I've seen it on just about every Carribean trip. My point was that while they could answer yes to the question, I wouldn't consider them a deco diver...

James

[DeepDiverBob]

I did the same thing a few weeks ago at Mermet. I was down 118 foot, and admit I was pretty narked out, and was only looking at my computer for PSI and for RBT. I for whatever reason didnt look at deco time. When I finally looked at deco, it was right as it went from 1 minute to 0. It didnt make me do a deco, but I immediately went to 60 feet for 2 minutes, then 30 for 3 minutes, then hung out at 15 feet for 10 minutes just to play it safe. Thanks for the tip on the rule of halves, Bill.

[theskull]

You gotta ask, because I think more people do that unplanned thing than do that planned thing. I've seen it on just about every Carribean trip. My point was that while they could answer yes to the question, I wouldn't consider them a deco diver...

James

Good point James, and though I quoted you I was not preaching at you, but broadcasting to all who might listen.

I have only seen deco diving, planned or unplanned, on 1 of my Carribean trips, and it was being done by the Divemaster who was trained and equipped for it. Every Carribean trip I have been on had strict limitations for max depth and no deco, and had a policy of grounding those who violated either rule. You need to find some better operators.

Today's computers will compute the necessary deco time to get you out of the water alive, but they do NOT display an optimum schedule of stops, only the shallowest one that is mandatory. Planning for deco also means planning exactly how much breathing gas you will need and ensuring that you can make the proper stops with a reserve. Loss of buoyancy control or being dragged to the surface by a buddy who loses control would be BAD.

NDL diving is very safe and most mistakes are not punished. Deco diving is very unforgiving and mistakes are not allowed.

theskull

[Atlaua]

I have only seen deco diving, planned or unplanned, on 1 of my Carribean trips, and it was being done by the Divemaster who was trained and equipped for it. Every Carribean trip I have been on had strict limitations for max depth and no deco, and had a policy of grounding those who violated either rule. You need to find some better operators.

You must not get to Cozumel much ;).

Seriously though, I do choose operators who take a more hands off approach. I prefer to be allowed to dive my own plan. Do they allow people to bend the rules? Yep, but every certified diver should be responsible for their own safety, it's not the DM's job to do it for you.

I've been on some boats that are like you describe and it just wasn't my cup of tea. But to each his own.

James

[DeepDiverBob]

But to each his own.


or her ;)

Sorry...had to do it.

[steve2281]

You must not get to Cozumel much ;).

Seriously though, I do choose operators who take a more hands off approach. I prefer to be allowed to dive my own plan. Do they allow people to bend the rules? Yep, but every certified diver should be responsible for their own safety, it's not the DM's job to do it for you.

I've been on some boats that are like you describe and it just wasn't my cup of tea. But to each his own.

James

My experience in Coz has been similar. On the cattle boats with big groups the profiles are very structured. However, on the six-packs or EDP (experienced diver trips) it's pretty much "anything goes".

[DeepDiverBob]

Granted, I have only beento Cozumel once, but on all the dives I did there, the only dive you could have gone and got yourself in a lot of trouble on would have been Devils Throat. Everything else was relativly shallow. Diving a computer, I ran out of gas before I ran out of bottom time.

[Atlaua]

Granted, I have only beento Cozumel once, but on all the dives I did there, the only dive you could have gone and got yourself in a lot of trouble on would have been Devils Throat. Everything else was relativly shallow.

That depends on the OP. IIRC you went on a shop trip to SCC. I'm guessing you were on the big boat?

Personally, it's not about deep for me, but looking at my logbook my first dives are almost all >90' there.

James

[cortez]

I think the question is ambiguous at best. Perhaps my biggest pet peave in this sport is the idea of a no-decompression dive. Every dive is a decompression dive, most dives performed within recreational limits are multi-level dives and should really be looked at more like staged deco dives than anything else. The reason I say most is because some dives actually are square profiled lacking the proper multi-level profile required for staged decompression. The models behind any set of tables considers your ascent time and safety-stops as decompression time assuming you are relatively relaxed (recreational remember) and fall into some categorization of an average diver...

All that being said, I treat a multi level dive similar to how I would treat staged decompression dive using back gas with one exception... no stage has a minimum required stop time. The purpose of each level is to allow off gassing and the longer one stays at each level the more one will off gas from the previous level.

DeepDiverBob, I'm not trying to be antagonistic. And I know what you meant by the question. It just bothers me that the dive industry gives such little - IMHO - education/explanation to why recreational dives are "No Decompression" dives. I think the current recreational systems really fail to prepare divers to properly plan their dive profiles. Furthermore, I think a little extra training in deco and table theory could help slant some of DAN (I think) calls table hits - those DCI hits that occur within table limits. If you look at the stats, most of those table hit profiles are pretty damn close to the alleged "No Decompression Limit".

[DeepDiverBob]

at the time of the posting, I dont think we had any tech divers on the board yet, and wanted to keep it simple, without doing any teaching. Just trying to get a feel of where everyone was at, and what kind of diving they was doing.

[theskull]

. . . I treat a multi level dive similar to how I would treat staged decompression dive using back gas with one exception... no stage has a minimum required stop time. The purpose of each level is to allow off gassing and the longer one stays at each level the more one will off gas from the previous level. . . .

Excellent addition to the discussion, Cortez.

At the Advanced Open Water level, anyway, most instructors are now teaching the 1-minute stop at half your max depth as part of a safe ascent.

Like you, I also treat almost all my dives deeper than 60 as deco profile dives. I will make a 1 or 2-minute stop (or swim for awhile) at about half the deepest depth, and spend some time at another 1 or 2 intermediate depths before making the 15-foot stop/swim.

theskull

[cortez]

... Like you, I also treat almost all my dives deeper than 60 as deco profile dives. I will make a 1 or 2-minute stop (or swim for awhile) at about half the deepest depth, and spend some time at another 1 or 2 intermediate depths before making the 15-foot stop/swim. ...

I think many more people would do the same if the idea of decompression where more thoroughly introduced in OW and AOW classes.

[Atlaua]

One little tidbit to clear up (Since you're being pickey Cortez :) ). Just because you ascend from one depth to another does not mean that you are offgassing. While it is true that you will be offgassing from faster compartments that are now supersaturated, you will still be ongassing to slower compartments that are still not saturated at the new depth.

James

[cortez]

Of course, that's a given. Anytime you breathe an compressed gas at depth - any depth - you are ongassing everything gas in the mix. For the sake of decompression profiling/modeling an ascent can be viewed as an attempt to offgas from the compartment which was controlling your ongassing at your last depth - believed at this time to be a fast to slow compartment transition.

But to really truly look at the benefit of offgassing at a specific depth versus continued ongassing, you must now be aware of the pressure gradiants in the depth change. This is the most accurate method for predicting when offgassing one compartment will overtake the ongassing of another compartment. To keep it simple, think about ascending from 100 to 92 feet offers some offgas benefit, but not much. Hence your computer may change your time staged deco obligation -or lack there of - by a minute, but the table doesn't differentiate. Now make the same eight foot change in 20 feet of water and see what it does.

Of course I'm just repeating information that everyone involved in this conversation already knows... very similar to my first post. I've only posted this and the original for those that haven't been fortunate enough to have any extended education - formal or otherwise - in decompression theory.

[Atlaua]

Of course I'm just repeating information that everyone involved in this conversation already knows... very similar to my first post. I've only posted this and the original for those that haven't been fortunate enough to have any extended education - formal or otherwise - in decompression theory.

Yes, and it's good to do so, which is why I was doing the same as well.

James

[theskull]

Another advantage of intermediate stops is control. Someone ascending from 100 ft. and intending to make a stop at 50 ft. SHOULD have less chance of his ascent rate getting away from him since he is aiming at becoming neutrally buoyant at that depth.

theskull

[jimini]

Deco diving is for a fully trainned diver to do, nobody else should even think about it. It involves much more than overspending your minutes below depths... It involves being able to react while being "Narced" and being able to overcome and be prepared to keep one's mind for self rescue. To plan the dive and gas consumption and the knowledge when to switch gases and for how long to breath that gas before switching again. It involves being trained by an Tec Instructior who will mend you into a proper complete tech diver without having to take unneccessary life and death chances...

Just remember "You've gotta be tough if you're gonna be STUPID"

jimini®

[theskull]

Deco diving is for a fully trainned diver to do, nobody else should even think about it. It involves much more than overspending your minutes below depths... It involves being able to react while being "Narced" and being able to overcome and be prepared to keep one's mind for self rescue. To plan the dive and gas consumption and the knowledge when to switch gases and for how long to breath that gas before switching again. It involves being trained by an Tec Instructior who will mend you into a proper complete tech diver without having to take unneccessary life and death chances...

Just remember "You've gotta be tough if you're gonna be STUPID"

jimini®

Actually, a properly trained tech diver will know his limitations and have planned his depth and gas so that he will NOT have to react while being narced. This is an important part of proper training. Yes, he will be experiencing some level of narcosis, but he will have selected that level and have had experience with well-practiced survival drills at that level of narcosis.

theskull

[jimini]

Isn't that what I said???

jimini®

[SLIM]

What is a fully trained diver? There are many out there that have been doing all kinds of Deco and cave dives that never took a class. Does that mean they are not trainied? Remember, someone had to do it and think of oh lets make a class on this and make more money so that ifyou do not hve the C-Card you wont be able to do special dives because you are not trained? Oh and if you are not trained this way then you wern't trained properly.

SLIM

[theskull]

What is a fully trained diver? There are many out there that have been doing all kinds of Deco and cave dives that never took a class. Does that mean they are not trainied? Remember, someone had to do it and think of oh lets make a class on this and make more money so that ifyou do not hve the C-Card you wont be able to do special dives because you are not trained? Oh and if you are not trained this way then you wern't trained properly.

SLIM

Wish you hadn't gone there. I agree with your complete point, but worry that too many will just focus on the "don't need a class" part of your statement.

How about rephrasing to "fully prepared diver"?

I know a very few divers without the card with whom I would make a planned deco dive--because they have the necessary skills, understanding, and equipment, and I trust them.

I also know more than a few who have the card but will not be making any serious dives with me as a buddy!

theskull

[SLIM]

You got me there TS I will agree with you about a perpaired diver. Yes there are any with the card that still do not understand the baisics that are more important. Then the ones that have only read books but have do not have the fundmentals down. There is a differnace between Certified and Qualified. To me a qualified diver is most likely going to be more knolwedgable then a ceritfied diver. Just remember the times have changed and the way we learn our skills has changed also.

SLIM

[DeepDiverBob]

Another thing to remember is that not everybody has their own compressors, and without those c-cards, you most likely cant get air, nitrox or trimix fills. Also, those handy little cards get you legal enterence into the cool places like RBD, Peacock and other state parks. Me personally, I like getting "official training." I am getting rather picky who I get my training from though. I like to get it from people that are doing the kind of diving that I am seeking the training for. I dont know anybody locally that teaches trimix, so when I am ready to take that step, I will be heading back to Florida to take that class from the same people that taught me cave. Now granted, just because you have the card doesnt mean you are automatically "trained" in every aspect of that kind of diving. I believe in being trained and experienced. You can buy training, but not the experience.

[Captain Brian]

Another thing to remember is that not everybody has their own compressors, and without those c-cards, you most likely cant get air, nitrox or trimix fills. Also, those handy little cards get you legal enterence into the cool places like RBD, Peacock and other state parks. Me personally, I like getting "official training." I am getting rather picky who I get my training from though. I like to get it from people that are doing the kind of diving that I am seeking the training for. I dont know anybody locally that teaches trimix, so when I am ready to take that step, I will be heading back to Florida to take that class from the same people that taught me cave. Now granted, just because you have the card doesnt mean you are automatically "trained" in every aspect of that kind of diving. I believe in being trained and experienced. You can buy training, but not the experience.
From someone in the wreck dive charter buisness if you do not have a cert card for deco, decompression dives will not be allowed. It is a legal issue and a safety issue. You may have the most experiance in deco diving in the world, but without the card I would have no way of knowing. The cert card shows that you have been properly trained and have the ability to dive safely. No tech instructor that I know would issue a card to someone who wasn't.

[CaptnDale]

I did not answer the poll because it did not have an appropriate answer for me. I do planned decompression dives regularly but docompression diving is not "great." Decompression is a tool that makes deeper, longer dives possible but it is not an end in itself. Decompression adds complexity and risk that is better avoided if possible and should be undertaken only with proper planning and training.

[theskull]

Hey Capt. Brian,

Thanks for resurrecting this old discussion. It was fun to read it again. You and Capt. Dale both make some great additional points.

BTW, DDBob did eventually find a local trimix instructor who does the dives as well as teach them, and is now one of my deep dive buddies. :)

theskull

[Captain Brian]

Hey Capt. Brian,

Thanks for resurrecting this old discussion. It was fun to read it again. You and Capt. Dale both make some great additional points.

BTW, DDBob did eventually find a local trimix instructor who does the dives as well as teach them, and is now one of my deep dive buddies. :)

theskull

Glad to hear that. Most of the shipwrecks that haven't been looted are in deeper water so to see pristine wrecks it will have to be a deco dive. The tech divers I know work very hard at keeping them pristine for future divers. Congrats to DDBob!!!