Would you really know what was going on if your computer went into Deco...?

[MikeFerrara]

It was under my response which suggested putting the computer rather than the diver into decompression. To refresh your memory:

Actually I was refering more to Dandy Dons suggestion than yours. Don didn't say anything about nitrox or a second computer/tables.

While reading the manual is fundamental, all diver training involves in water practice? You wouldn't consider a diver well trained in advanced deco techniques if all he did was read a manual, no matter how well he understood the material.

Yes in-water training is needed. I pointed out some of the skills that a diver should in my opinion (and the opinions of the agencies I teach for) have before incuring a decompression obligation even by accident. I think they're good things to learn and there are lots of divers that con use some learnin on them.

If diver wants to more fully understand his instruments and the contingencies available in recreational diving your efforts would be better spent suggesting ways to safely obtain the experience. Recommending complex multi-gas advanced deco training does little to help a purely recreational diver. Most are unlikely to take such a course and would quickly forget the unused skills if they did.

Ralph

That's really sort of what I was doing. I really think that a divers who's going to dive any where near a no-stop limit (or even those who aren't) should learn something about decompression theory beyond red light/green light on a computer.

I also think that all divers and especially divers nearing a no-stop limit should understand gas managent beyond "be back on the boat with 500psi". Unfortunately the agencies don't seem to be teaching gas management until decompression training si I thought I'd mention it.

A decompression obligation is considered a virtual overhead and for overheads redundancy (at least in breathing gas) is recommended by pretty my everyone.

While I wasn't suggesting that every one reading this thread needs to strap on a tank of decompression gas I don't see the sense in doing dives that will take you anywhere near a no-stop limit without understanding the advantages of it. Personally (and you can do what you want of course) but it would be a rare occassion that I venture very deep for very long without a decompression gas.

In my opinion (underline that if you wish) standard recreational equipment and the methods commonly taught are NOT suitable for dives to 100 ft and beyond. I really don't care what PADI (or some other agencies) is doing because I keep seeing them hauled out of places like Gilboa in ambulances.

The training that I recommend to my students (and any one else who asks) who want to go to 100 ft is courses in the catagory of the IANTD advanced nitrox or GUE's recreational triox. These are recreational classes (not considered technical by these agencies max depth of 130) that prepare the divers skills and introduce the equipment and planning techniques that make a dive like this really enjoyable rather than something on the edge of being a fire drill. With this training a diver wouldn't be worried in the least about incurring a few minutes of decompression on accident.

What does DAN say the average ascent rate of a recreational diver is from 15 or 20 feet to the surface? Something like 180 ft per minute? This can hose you on any dive but when many computers clear you to surface after even a little decompression you'll be at or near the mac allowable loading which is why the computer book probably tells you to discontinue diving. Anyway this is no time for a rapid ascent in the final stage and that's the norm. And this is the place to start preparing for significant gas loads rather than the computer display and that's why I mentioned the development of shallow water skills.

Now I don't care if a diver prefers to take a class or learn it on their own like Genesis but this is in my very strong opinion the knowledge that a diver should have before going to those depths where busting an NDL is a significant risk.

Over the course of all my diving and all my teaching this is the conclusion that I've come to. I can give literally hundreds of examples of things that I've withnessed in the water to illustrate how I came to this conclusion. I probably feel more strongly about this than any other single subject in diving. I've just seen too many divers at 130 ft who really should have been at 20 ft learning to control their buoyancy. Oh, and they often shoot to the surface and clear the water to their waust when a little thing like a free flow happens. Sometimes they get hurt and sometimes they don't. Their computer display really may be the least of their worries.


Maybe I'll start a seperate thread on dealing with deep "recreational" diving.

ok so some of the stuff I brought up is beyond the scope of the original question. It's just that addressing the original question without the rest makes absolutely no sense to me and it's not likely that most diver will hear it in their Advanced Open Water Resort diving class.

 

[voop]

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I was just refering to what people have said throughout the years. Just last summer I ran across a guy that would of has 2 weight belts if he could. He even had 2 slates, 2 marker buoys, 2 masks and a bunch of other stuff.

I like your way of thinking. Some people load up like a week long cave dive for every dive they do.

<SNIP>

Gary D.

Actually, if you want to do deco, redundancy is a good idea. It's really hard to keep a stop if you loose all your weight -- even if you have a line to hold on to. I do not wear two weight-belts, but I always distribute my weight such that I can't accidentially jettison all of it (i.e. "weight-integrated BC w weight in more than one pocket" or "weight-harness + weightbelt" or some such thing.)

Same goes for masks...I always carry two of them. It *is* possible to use the "air bubble" to allow your eyes to focus on your timer/depth gauge/deco plan/computer, but it is all else equal easier with a mask.

When I did my deco training, the instructor had us hold a 5m stop for 20 min without a mask and no line to grab onto -- and an allowed depth variation of +/- 1m. The same guy had os try to hold a 5m stop without weights atall. Both basically to prepare us for a "worst-case" scenario, which would be to have a deco-obligation and somehow a basic tool malfunctioning. Or, if you wish, to examplify why redundancy is good. Yes, I do carry two DSMB's too, but they serve a signalling purpose when used together.

As for loading up for a "week long cave-dive" -- well, DSMB's are not that usefull in a cave For me, I prefer to load up in the same way for all my diving, even the easy nice shallow warm pretty short OW-ones. I hope that should the brown stuff hit the fan, then I will be in familiar equipment which I know every detail of -- and my task-loading will not consist of "where did I put the now urgently needed gadget X?".

Ok, I do not bring the drysuit to the tropics, and the amount of gas I bring depend on the dive I'll be doing, but otherwise I kit up in the same way for everything. It's not really as "bulky" or "extreme" as you may think. And yes, I have once saved a nice shallow tropic dive where my mask-strap broke when adjusting it under water, through reaching for my redundant mask I could have surfaced directly, though, but it was nice to just continue

This is not really special -- dealing with possible "worst-cases" in training: a PADI OW student is taught to breath from a free-flowing regulator. One might argue, that one should always dive with gear well-maintained and free from free-flows, but planning for a contingency (the potential for a free-flow) is just prudent. Same thing: bringing redundant gear is just preparing for a contingency.

 

[truva]

How exactly would you go about knowing which "bad thing" is going to happen to you?

I personally prefer to plan on a worst case scenario and anything less is a cakewalk.

That's a dumb question from someone that I'd think would know better with a name like Cave Diver.

Which "worst case" scenario are you planning on?


Truva

 

[rcohn]

Actually I was refering more to Dandy Dons suggestion than yours. Don didn't say anything about nitrox or a second computer/tables.

[snip]

In my opinion (underline that if you wish) standard recreational equipment and the methods commonly taught are NOT suitable for dives to 100 ft and beyond. I really don't care what PADI (or some other agencies) is doing because I keep seeing them hauled out of places like Gilboa in ambulances.

The training that I recommend to my students (and any one else who asks) who want to go to 100 ft is courses in the catagory of the IANTD advanced nitrox or GUE's recreational triox. These are recreational classes (not considered technical by these agencies max depth of 130) that prepare the divers skills and introduce the equipment and planning techniques that make a dive like this really enjoyable rather than something on the edge of being a fire drill. With this training a diver wouldn't be worried in the least about incurring a few minutes of decompression on accident.

[snip]

Over the course of all my diving and all my teaching this is the conclusion that I've come to. I can give literally hundreds of examples of things that I've withnessed in the water to illustrate how I came to this conclusion. I probably feel more strongly about this than any other single subject in diving. I've just seen too many divers at 130 ft who really should have been at 20 ft learning to control their buoyancy. Oh, and they often shoot to the surface and clear the water to their waust when a little thing like a free flow happens. Sometimes they get hurt and sometimes they don't. Their computer display really may be the least of their worries.


Maybe I'll start a seperate thread on dealing with deep "recreational" diving.

I'm glad I don't dive in your area! I must have witnessed thousands of dives and I've never seen a diver shoot to the surface to their waist or even seen a single decompression/AGE related injury. The vast majority of divers I've seen perform safety stops and monitor their computer or tables. Many are beginning to incorporate deeper stops. All of us need to work on buoyancy control, but most experienced divers (except for some of the NE lobster divers I know) do a reasonable job.

I do agree that most divers underestimate safe levels of gas reserves and many hanging on the line during safety stops fail to notice the depth variations their weight is causing.

If you want to present yourself as a scuba professional and diving authority, you need to provide some form of proof to back up your extreme assertions. What statistics support you claim that advanced deco gasses are necessary on all dives to 100 ft? Millions of recreational dives are being conducted to that depth, where are all the accidents? How many injuries would results from recreational divers accidentally breathing the wrong mix at depth? Vastly more experienced tech divers make this mistake, I would expect it would occur more often in the recreational market. What are the chances that recreational divers could safely recover a diver in convulsions? Recreational training standard teach divers to directly bring an unconscious diver to the surface. Instructors and divemasters would be liable for violating their standard of care if they held a diver at depth until the convulsions stopped as the DIR/GUE system teaches.

To change the recreational diving system you would need to show that a problem in fact does exist and that your proposed is actually a safer way to dive (doesn’t create greater dangers than previous practice).

Ralph

 

[diverbrian]

I'm glad I don't dive in your area! Millions of recreational dives are being conducted to that depth, where are all the accidents? How many injuries would results from recreational divers accidentally breathing the wrong mix at depth? Vastly more experienced tech divers make this mistake, I would expect it would occur more often in the recreational market. What are the chances that recreational divers could safely recover a diver in convulsions? Recreational training standard teach divers to directly bring an unconscious diver to the surface. Instructors and divemasters would be liable for violating their standard of care if they held a diver at depth until the convulsions stopped as the DIR/GUE system teaches.


Ralph

Early in my SSI Nitrox training (which was done in conjuction with my OW training), the video there recommends holding the convulsing diver at depth if possible and they also admit that it is a "between the devil and deep blue sea" choice in the choice between embolism or drowning.

As for needing advanced Deco mixes to go below a hundred ft. I happen to agree with you, but I typically take my stage with me on those dives since I have the training doing a safety stop on EAN50 can't do anything but help. It is not a need, but as decompression is an inexact science, I will take most anything that helps to keep me out of a chamber.

Much of this is a healthy diversity of opinions. That is where improvements are made. Where I disagree is your statement about the possibility of a recreational diver reaching for the wrong mix. That sounds too much to me like the arguement that recreational divers couldn't use nitrox because they wouldn't be responsible enough to stay within MOD's. I haven't seen divers dropping from Oxygen Toxicity and most of the people that I dive with use nitrox.

 

[-hh]

Suunto's dive computers are actually quite good, as far as their deco algorithm, for an air or nitrox dive. I have found DCIEM deco tables for air dives to be the most conservative. If you compare Suunto's dive simulator for a deco dive on air with DCIEM, you get quite similar data.

IMO, the Suunto's have too many "hidden rules" which make them unsuitable for even mild deco...duration of Surface Intervals, etc. I had mine on a dive where it demanded ~20 minutes of deco when any other model I know of would have only required 0-7 minutes. What made it even more incredulous was that time hanging at ~17fsw didn't provide any meaningful credit (~1 minute reduction per ~5 minutes of hang!) - - it only ticked down by hanging at ~11fsw (literally!). It was quite rediculous in its conservatism to the point that it actively encouraged violation...it tempts me to go back to my EDGE

But the whole point is to stay clear of deco whenever you are diving with a computer, rather than with preplanned slates...

And "thank-you PADI" for redefining "REC" this way many moon ago and creating this problem that any deco whatsoever is purest Evil.

...and multiple deco gasses

Helpful, but not absolutely necessary.

I suppose that is where non-tech divers get confused, when they see that their dive computer is set up to handle deco, but there is no way to communicate to the divers the dangers of deco, unless they take a deco class.

Conversations like this can communicate the risks - - no class required. The problem is that particuarly within the Rec context, the risks of Deco aren't all that great until the deco obligation becomes significant, which is modestly unlikely, and it is a disservice to claim that they are profoundly more hazardous than other preexisting risks that are present and accepted on Rec dives. For example, consider a dive to ~100fsw and the risk implications of:

a) Dive duration right to the No-Deco Limit, followed by a rapid (uncontrolled) ascent all the way to the surface...

- versus -

b) Dive duration of a few minutes longer (resulting in a ~5 minute Deco Stop as per the same Table that said the above was a No-Stop dive), followed by a normal/safe/controlled ascent to deep stops, but the ~5 minutes of required deco @ 10fsw is skipped, and the diver proceeds slowly to the surface. Otherwise, there were no ascent violations throughout.

The reason for this example is because first is clearly an issue with all Rec diving, and the second is effectively claimed to not be. However, from a total risk perspective, which one is really the "lesser evil"?

I know which one I'd pick.


-hh

 

[ArcticDiver]

From your post Mike: "While I wasn't suggesting that every one reading this thread needs to strap on a tank of decompression gas I don't see the sense in doing dives that will take you anywhere near a no-stop limit without understanding the advantages of it. Personally (and you can do what you want of course) but it would be a rare occassion that I venture very deep for very long without a decompression gas."

Now I'm a Newbie on this Board and so I don't really know you very well. So yank me up short if I'm misinterpreting what you seem to say on this subject.

You seem to say that anyone who Really Knows about Deco will always take Deco Gas with them on any deep dive(depth unspecified), or one that might take a person even close to Deco.

I submit that the purpose for Deco Gas is to shorten mandatory deco time. So, if you are making a dive where you only incur a short deco time and have plenty of back gas why carry along another tank? Just enjoy the extra time in the water.

Now again I may be misinterpreting but you seem to have a low opinion of most other people's ability to make good decisions about this subject. Your language seems to say that people will "rush" I think you said to the deco ceiling and wait out the mandatory time. I don't know what you mean by rush. The way most folks were taught I think is to Slowly ascend to the Deco Ceiling and then hang out until cleared to ascend further. I think most folks do exactly that, make careful ascents.

Now I fully agree there is more than one way to dive safely and have fun doing it. If you aren't having fun there isn't a lot of reason to dive. But you don't seem to say that.

Please clarify so I can understand.

 

[MikeFerrara]

I'm glad I don't dive in your area!
If you want to present yourself as a scuba professional and diving authority, you need to provide some form of proof to back up your extreme assertions. What statistics support you claim that advanced deco gasses are necessary on all dives to 100 ft?

Where did I say that advanced decompression gas is required to dive to 100 ft?

divemasters would be liable for violating their standard of care if they held a diver at depth until the convulsions stopped as the DIR/GUE system teaches.

Actually the recommendation to do this can also be found in the PADI nitrox text.

To change the recreational diving system you would need to show that a problem in fact does exist and that your proposed is actually a safer way to dive (doesn’t create greater dangers than previous practice).

Ralph

I don't need to show proof of anything. The classes that I mentioned are designed just exactly for what I recommend them for and teach the skills that those agencies believe that a diver should have to do dives of that level. I'm not trying to really change anything. I'm just encouraging that option.

Using the IANTD advanced nitrox class as an example because I'm most familiar with it...the class envolves diving to a max depth of 130 ft and a max manditory decompression of 15 minutes. Isn't that the kind of dive we're talking about pretty much?

But...the focus of the class is the skills that serve a diver doing deeper recreational dives.

 

[MikeFerrara]

You seem to say that anyone who Really Knows about Deco will always take Deco Gas with them on any deep dive(depth unspecified), or one that might take a person even close to Deco.

No. I'm saying that I think it's a good idea to understand the advantage of it before deciding not to. I almost always decide to use the decompression gas. Rarely but for some dives I decide to leave it behind. I have the choice though and I have done enough decompression that I have a feel for what I can get away with in the range of profiles that I can dive.

I submit that the purpose for Deco Gas is to shorten mandatory deco time. So, if you are making a dive where you only incur a short deco time and have plenty of back gas why carry along another tank? Just enjoy the extra time in the water.

ok first I would like to do away with the term "NDL" all together. Once we get near it (since we're having such a hard time getting rid of it) we're in a grey area. On one side of the line (that doesn't really exist) we're statistically pretty safe within the range of the testing of the model. Divers do sometimed get bent there though.

A freind of mine was badly bent doing a 100 ft dive where he had a short decompression which he did according to his computer. He is a very good diver btw with as much control in the water as any one I know. He and his buddy puzzled over why he was bent. They provided me with the profile details. I ran the profile in several different decompression softwares and depending on how I set the user settable parameters I could generate a profile that ranged from requireing no mandatory decomression to a schedule that required about 25 minutes more than what they did.

If I had done the dive they did there is no way I would have dived that schedule. What's the point? The point is that different tables and different computers give drastically different answers. Which one (if any) would you use if you had your choice? How many in this thread baught their computer planning on using it for staged decompression and have chosen that schedule?

One purpose of decompression gas is to shorten decompression but why focus on length. What I want is good decompression. I want to be able to carry my gear up the hill to the truck without bending myself.

So...after having spent some time educating myself on decompression I have made choices about how I want to do it.

Do you prefer to make those choices or to just get into deco and hope the guy who wrote the firmware made the right choices for you?

Now again I may be misinterpreting but you seem to have a low opinion of most other people's ability to make good decisions about this subject.

I don't know about most people but I'm only too familiar with what's taught in the training that "many" divers have and I'm afraid they weren't prepared to choose a decompression methode which I think is important even on a dive with a little bit of deco. They weren't taught much about gas management either.

Your language seems to say that people will "rush" I think you said to the deco ceiling and wait out the mandatory time. I don't know what you mean by rush. The way most folks were taught I think is to Slowly ascend to the Deco Ceiling and then hang out until cleared to ascend further. I think most folks do exactly that, make careful ascents.

First off in the training we're talking about, the diver was taught to not do into decompression. They were also taught some rule of thumb emergency decompression procedure in case they needed it but this emergency procedure is designed so that some one who's not smart enough to really understand can get through it.

In this case I was refering to the ascent speed that many divers are taught as rushing when we're talking about ascending to the ceiling displayed by most computers. What is this ceiling? On a computer using a haldanian model it's the shallowest depth that that the diver can ascend to without resulting in a gradient greater than the critical tension of the leading compartment right? This completely ignores everything we know about bubble mechanics. Meaning that we now know that this large initial gfradient does produce/allow the growth of bubbles. By aplying gradient factors or using a bubble model we smoothen that curve and minimize that large gradient caused by the far initial ascent. We also decide what percentage of the critical tension of the controling compartment we want to tolerate when we surface.

If you use a decompresion table streight you surface at 100% of that final controling compartments critical tension. I use 85% and started with 70%. I know divers who use 100%

The point to all that is to try to say you couldn't pay me enough to slowly ascend to some recreational computers ceiling and sit there until it told me to move up. Because in this case slowly ascending to that ceiling is to me (and others) rushing. Some might be ok with it but I think it's best to know what you're ok with don't you?

BTW, these "M" values or critical tensions are about as dependable a boundry as the NDL. They work most of the time all else being equal (which it isn't always)

Now I fully agree there is more than one way to dive safely and have fun doing it. If you aren't having fun there isn't a lot of reason to dive. But you don't seem to say that.

Please clarify so I can understand.

By all means dive how you want and have fun. However I have to continue to recommend that divers who haven't dug into this stuff try real hard to avoid extreme inert gas loads until they do.

Once they do they may decide to decompress exactly as their computer says to. Then again they may not but until they make the decision they're letting some one else make the decisions for them and it isn't me.

 

[MikeFerrara]

Let me ask every one something...

Using a haldanian model computer what's the differene in gas loading when you are at the leading compartments critical tension after 5 minutes of required decompression and being in the same situation after 30 minutes of required decompression?

Which holds more risk and why?