Square Profile Dives

[IndigoBlue]

Jerryg once bubbled...
..."NEVER use your COMPUTER or any other dive computer for repetitive "square profile" dives (dives to the same or nearly the same depth) deeper than 60 feet (18m). This is an unsafe diving practice which will greatly increase your risk of DCS, regardless of what your COMPUTER reads."

BRW's NAUI RGBM Deco Tables state the following caveat for all repetitive diving, whether air, nitrox, trimix, helitrox, SCR/CCR and whether NDL or deco:

"REPETITIVE DIVES MUST BE A MINIMUM OF 30 FSW SHALLOWER THAN THE PREVIOUS DIVE."

Perhaps he can comment on his findings related to this rule, which Mares seems to be cognizant of as well. By the way, there are additional caveats as well by BRW.

Great diving manual ! I highly recommend it. $100 bucks only.

http://www.naui.org/index-side.html

 

[chrpai]

Which conflicts with latest studies saying that deepest dive first isn't nessecary.

 

[IndigoBlue]

chrpai once bubbled...
Which conflicts with latest studies saying that deepest dive first isn't nessecary.

Were we to try to agree on a definition of "latest studies" I would stipulate BRW's studies. Therefore the conflict would be within your own statement, and not with BRW's findings.

Quite frankly, I know of no studies that are more recent than BRW's are. The flip side of that coin is that BRW may indeed be considered to be avant guard, way ahead of his times. I guess the only way you can find out is to find out for yourself.

Diving theory is always changing. It should change. Our technology to understand it changes too.

 

[Charlie99]

IndigoBlue once bubbled...
BRW's NAUI RGBM Deco Tables state the following caveat for all repetitive diving, whether air, nitrox, trimix, helitrox, SCR/CCR and whether NDL or deco:

"REPETITIVE DIVES MUST BE A MINIMUM OF 30 FSW SHALLOWER THAN THE PREVIOUS DIVE."

Perhaps he can comment on his findings related to this rule, which Mares seems to be cognizant of as well. By the way, there are additional caveats as well by BRW.

It appears that there is a wide variety of opinion in this area.

Yet another well-recognized diver has this to say about repetitive dives:

"This area of the discussion needs to be prefaced by a couple of important reminders. One, keep in mind what I said about the level of offgassing in bubble form when the move is made to 1 ATA at the surface - this can be a real shower of bubbles if you do not follow the ascent recommendations that I made. Be that as it may, the other important point is the bubbles tend to GROW post dive as they take like gas in from around them. They peak in size and then diminish. This is all relative. If you look at decompression folklore, like what IANTD teaches, you will see references to bubbles peaking in size and frequency up to four hours after a dive. First of all, this applies more to people who should not be diving in the first place, and secondly it applies to air diving where there is no adequate way to decompress.

In my case, I totally clear of any signs of bubbles from the most horrendous dives in 30 minutes or less. That is what you should shoot for, but more importantly, shoot for no bubbles to start with by following my final ascent guidelines. Bubble growth is fact life. Showering bubbles post dive is a screwup.

As far as "residual nitrogen" or helium or whatever, this is a non-issue. It is inherently more true for nitrogen since we are full of it anyway, but the fact is the only consideration you have to give to repetitive dives is in the concept of ascent once you have taken a surface interval and may be still bubbling - you have to be far more careful about your ascent rate on a second dive due to this effect. See my article on "why we do not bounce dive" for all the reasons.

Otherwise, repetitive diving is a good thing, and you should do your shallower dive first and then your deeper one. The stupidity taught in that regard is beyond the pale." (emphasis added)

http://www.wkpp.org/articles/Decompression/repetitive_dives.htm

 

[IndigoBlue]

This is possibly turning into a nice verbal brawl.

Before it gets out of hand, let me just say that I believe BRW has some great ideas, and I am going to spend the next couple of years validating them for myself. That does not make him God, and I do not believe in the Spanish Inquistion for heretics either.

Believe whatever you want to believe, and let others do so as well.

Or, like James Bond said, "Live and let die."

 

[chrpai]

IndigoBlue once bubbled...
This is possibly turning into a nice verbal brawl.

Before it gets out of hand, let me just say that I believe BRW has some great ideas, and I am going to spend the next couple of years validating them for myself. That does not make him God, and I do not believe in the Spanish Inquistion for heretics either.

Believe whatever you want to believe, and let others do so as well.

Or, like James Bond said, "Live and let die."

Funny, I don't think anyone has attacked your beliefs here. I just pointed out that other recent studies have said deep first can be rethought. Your guy says the opposite. Big deal, it's all theory. Can we not talk about it, or have you already labeled us heretics and decided that you don't want to talk about it?

 

[cornfed]

chrpai once bubbled...

I just pointed out that other recent studies have said deep first can be rethought.

What are the studies? You can't simply say they exist and expect everyone to agree with you.

 

[IndigoBlue]

chrpai once bubbled...



Funny, I don't think anyone has attacked your beliefs here. I just pointed out that other recent studies have said deep first can be rethought. Your guy says the opposite. Big deal, it's all theory. Can we not talk about it, or have you already labeled us heretics and decided that you don't want to talk about it?

It just looked like it might become a brawl.

I did not read between the lines in your posts, so I did not infer what your affiliations were.

I see positive contributions by all of the major diving organizations, YMCA / NAUI / SSI / PADI / IANTD / ANDI / TDI / GUE etc.

 

[chrpai]

cornfed once bubbled...


What are the studies? You can't simply say they exist and expect everyone to agree with you.

I take it you don't know how to use the search button or read any diving publications do you? Are you really that ignorant or you just trying to be a pain in my tush?

"Reverse Dive Profiles Workshop" conducted at the Smithsonian Institution sponsored by American Academy of Underwater Sciences, DAN and DEMA among many others

Their findings:

Historically neither the U.S. Navy nor the commercial sector have prohibited reverse dive profiles.


Reverse dive profiles are being performed in recreational, scientific, commercial and military diving.


The prohibition of reverse dive profiles by recreational training organizations cannot be traced to any specific diving experience that indicates an increased risk of DCS.


No convincing evidence was presented in the workshop that reverse dive profiles within the no-decompression limits lead to a measurable increase in the risk of DCS.


The attendees found no reason for diving communities to prohibit reverse dive profiles for no-decompression dives less than 40 meters (130 feet) and depth differentials less than 12 meters (40 feet).

 

[MikeFerrara]

chrpai once bubbled...



I take it you don't know how to use the search button or read any diving publications do you? Are you really that ignorant or you just trying to be a pain in my tush?

"Reverse Dive Profiles Workshop" conducted at the Smithsonian Institution sponsored by American Academy of Underwater Sciences, DAN and DEMA among many others

Their findings:

Historically neither the U.S. Navy nor the commercial sector have prohibited reverse dive profiles.


Reverse dive profiles are being performed in recreational, scientific, commercial and military diving.


The prohibition of reverse dive profiles by recreational training organizations cannot be traced to any specific diving experience that indicates an increased risk of DCS.


No convincing evidence was presented in the workshop that reverse dive profiles within the no-decompression limits lead to a measurable increase in the risk of DCS.


The attendees found no reason for diving communities to prohibit reverse dive profiles for no-decompression dives less than 40 meters (130 feet) and depth differentials less than 12 meters (40 feet).

In the abaove quote this...

The attendees found no reason for diving communities to prohibit reverse dive profiles for no-decompression dives less than 40 meters (130 feet) and depth differentials less than 12 meters (40 feet).

Is the important phrase. BRW participated in the workshop and is quick to point out that beyon the above stated conditions the significance of reverse profile is very different.

Disloved gas models do not take all the effects of a reverse profile into account. I think you can get away with it within the above stated limits only because of the small inert gas load.

Naturally the magazines and people in general have done a great job of misquoting the results of the workshop by shortening it to..."reverse profiles are ok now".

It was funny. I still had the shop when the results of the worshop were were published. I of course read what all the magazines printed, including DAN. All of a sudden I had divers comming asking me if I'd heard that reverse profiles were ok because we use computers now and junk like that.

As for the GI quote...well he says a lot of thing that no one seems to be able to make any sense out of (of the ones who really try). He may have some anectdotal (sp?) eveidence which can fool you in a hurry and a great sense of showmanship.