15' Safety Stop vs Minimum Deco

[AquaTec]

Mike some quick thoughts on your excelent post

MikeFerrara once bubbled...
One of the things I find difficult about teaching diving is matching my own views to agency views. I dislike terms like "NDL" or "no decompression diving". What are you supposed to do with the extra inert gas?

it is the term that is wrong - NDL or No decompression diving comes from the opposite, meaning Decompression diving.
in other words these dive do not require any deco stops.
it is not to say that a dive is not ongassing Nitrogen, they are just maintaining a time and depth that allows them a direct ascent to the surface without having to offgass first.

Take it home with you?

yes then they take it home with them, probably feeling a little sluggish

an entry level class it is hard to teach deco procedures

That is beacause they are still trying to figure how they will clear their mask and not freek out. diving is a journey, don't try and get them to far down the road yet

One of the things I do, however, is to point out what a recreational dive table says about a 130 ft dive and then give an overview of how I would do that dive. I give a brief description of the gases used, equipment used, gas planning and my ascent schedule. I don't call it minimum deco.I run the schedule with any one of a number of dive planning softwares. You see, I believe that 130, 100 or whatever is too deep for the vast majority of recreational divers especially given the equipment and level of planning being used. Some see that if a dive is too deep for me, with that equipment and those methods, then maybe they should think twice

I am not sure what agency you teach for, but i do like PADI's method of progressive training, OWD = 60ft, AOWD = 100 feet, Deep specialty = 130 feet this way they are not trying to run before they can walk, a discution in deeper diving is good as long as its not instructional at the OWD level. keep the training within the level they are at.

For a "shallow dive" a "minimum deco" schedule will not yield a statistical advantage in avoiding DCI symptoms. I am sure there is a difference in bubble presence and size but does it matter?

no but a safety stop will

I don't know of an agency that dismisses the value of deep stops, however they do not, at this time, teach the theory to divers who haven't yet made a dive. I let new divers know such theories exist and of my beliefe that knowlege of them is a prerequisit to "deep" diving. In the context of recreational diving, my definition of deep is not very deep.

I start to introduce the fact that these theories exeist in the advanced class, as they are doing dive to 100 feet. but i don't elaberate on them to much. i just point them to my library and mention that beyond a hundered feet they should read all those books first. several 100 of them are on the shelves

good post for discution Mike

(Edited for readability... hopefully I got it right. -Spectre)

 

[Jarhead]

recently in the Ask Dr. Decompression forum and Bruce Wienke himself (Mr. RGBM) got involved. It's well worth going back and reading. Mr. Wienke (I hope I'm spelling his name right) included links to some PDF papers that been published.

Based on that, I'll stand with the deep stops.

Couple of points though.

1.) New divers can learn bouancy control enough for the deep stops. My son is very new. Just certified this summer and only has seven dives in the book. But he can still do stops at 30, 20, & 10 fsw (and in a current to boot).

2.) All dives are decompression dives. The amount of decompression required maybe negligable (spelling), but it's there. Some agencies do recognize this (NASE). Familiarity with the decompression dive tables (NAVY deco tables) is still taught in Basic OW class. They do not condone them, but they think you should know what they are and why you shouldn't do them. Unfortunately they don't use tables with deep stops though.

Jarhead

 

[AquaTec]

spectre
thanks for the help.
I haven't figured out how to do that type of formating yet

 

[Uncle Pug]

raxafarian once bubbled...
UP...how long you gonna leave us hanging

More than the answer is revealed by waiting.

 

[raxafarian]

Confucius says...

 

[The Iceni]

Uncle Pug once bubbled...
Which is better: a 15' safety stop or Minimum Deco of 1 minute at 30', 20', 10' for recreation NDL dives?

Trick question Uncle Pug!

By definition, if there were such a thing as a No Decompression Limit dive the diver would have no need to perform any stops at all, but of couse no such dive exists.:bonk:

On the other hand, might I suggest that - in theory at least - in order to reduce micronuclei formation that the rate of ascent should simply be reduced as the diver ascends to maintain a constant, safe rate in pressure change. Are not stops simply a practical way of achieving this?

As an aside;-

Buhlmann ZHL16
Number of compartments: 16
N2 half-times(mins):
4.0, 8.0, 12.5, 18.5, 27.0, 38.3, 54.3, 77.0, 109.0, 146.0, 187.0, 239.0, 305.0, 390.0, 498.0, 635.0

It would seem that for every NDL dive shallower than 60 feet lasting less than 20 minutes say, compartments 7? to 16 will be ongassing at all stages of the dive so any delay in surfacing simply increases the post-dive nitrogen load.

So, to my simple mind the fewer stops the better and one at 10 feet would be the optimum.

 

[Uncle Pug]

Dr Paul Thomas once bubbled...
Trick question Uncle Pug!

BTW Paul... I am sure that you already ran the figures on the short duration shallow 60' dive and are aware that for all compartments tissue loading doesn't vary all that much during the whole ascent which ever way you do it

 

[Soggy]

Uncle Pug once bubbled...
~Thanks to Aaron for the question~

Question:
Which is better: a 15' safety stop or Minimum Deco of 1 minute at 30', 20', 10' for recreation NDL dives?

Please give your reasoning and/or supporting evidence.
Remember the forum is Basic Scuba Discussions.

Trying to pass the blame, eh?

So far, I haven't seen any factual evidence that this minimum deco procedure would be better than a 5 min safety stop at 15'. However, intuition tells me that it probably is a better procedure, as you are simply slowing your ascent. It also would seem to be a good procedure if one is planning to do deco dives in the future...practicing the bouyancy control that staged deco requires certainly can't hurt.

All in all, I think I will consider trying this. The trick is convincing a buddy to do the same. Since the procedure includes a safety stop as defined by the agencies (3-5 minutes at 10'-20'...3 mins at 10' satisfies this requirement), I believe that this procedure cannot hurt....still waiting for the evidence, though.

 

[jonnythan]

A minute or two at each of 30', 20', and 10' is better because it gives you a chance to practice some precise water column control every dive.

 

[Uncle Pug]

AaronBBrown once bubbled...
Trying to pass the blame, eh?

So far, I haven't seen any factual evidence that this minimum deco procedure would be better than a 5 min safety stop at 15'.

Well I figured it would be better to get this portion out of the *thirds* thread so as not to confuse either issue.

the answer concerning *proof* has already been flushed out but let me amplify it:

If we are talking about theoretical tissue compartment loading and off-gassing then there is really no appreciable difference in the end result using either method... even when used on various depth/duration dives within the recreational limits.

In fact there really isn't a big difference in tissue compartments at any point during the process if both methods are compared side by side.

So why did I say the minimum deco was *better*- *a better way* - *more progressive*?

(Besides bait for what turned into this thread )

The answer to that has already be mentioned in this thread as well though maybe not in the exact words that I am going to use:

1. Discipline in slowing the ascent.
2. Training in buoyancy control and timing.
3. Feeling better after the dive... not theory but subjective exp.
4. Starting the process deeper in case you need to abort.

Another thing that I find might be helpful about the minimum deco concept is to insure that divers actually do the stop. How many folks get bored after the first minute or two and omit the full 3~5 at 15'? No need to protest that you always do the full time... that isn't the issue... in reality how many divers do this?

However that said... I see benefit in doing the 3 or 5 at 15' but not the 3~5.

Since it is harder to discipline oneself to do the longer stop it is great for training if you force yourself to do a predetermined amount of time there... pick your number 3, 4, or 5 and then do exactly that.

Now all of this is just my opinion and it is in the take it or leave it department. You certainly won't hurt yourself trying any of this.

Then you be the judge.