Dive Problem: Dive Shallow then deep

[Bob DBF]

According to the General Rules section of the RDP, "Plan repetitive dives so each successive dive is to a shallower in depth"

The RDP tracks two tissue compartments when you do deep dives, and follow them with repetitive dives. The first is the controlling compartment for the first dive. The second is the 1 hour compartment. The compartments in between is not accounted for, and neither are the slower compartments. The rules in the RDP are there to ensure that none of the other compartments become controlling compartments when you are using the tables, and if they do, they will be accounted for by the times for the particular depth in the table. So, yes, it is possible by not following all of the RDP rules to end up in Deco even though the table says you are not.

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Exactly, and if the table rules do not allow a particular dive profile, other methods must be used to calculate the profile in order to assure it is safe.

Thanks.

I lucked out because I had not even seen the new tables untill after I was computer diving. I'll just go back to the Navy tables I was diving before, when I'm not on computer, parts of them are stuck in my head anyway.



Bob
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I may be old, but I’m not dead yet.

 

[DevonDiver]

What you are describing are reverse profile dives.

You are confused. A 'reverse profile dive' describes (uncannily) the profile of a single dive, not a series. Where a 'normal' or 'conventional' dive profile would indicate an immediate ascent to maximum depth, followed by a gradual ascent from that portion.... a 'reverse profile'... is, well, the reverse of that. A slow ascent, with achievement of maximum depth occuring in the later portion of the dive.

As many cave and technical wreck divers know... the adherence to 'ideal' dive profiles isn't always practicable if your route/depth is dictated by passage though an overhead environment. I'm not aware of any particular issues/incidents that have been attributed to 'non-traditional' dive profiles... other than the common sense in their use in relation to current decompression theory.

If discussing a reverse order to a dive series (shallower followed by deeper dives), the general advice given by most scuba agencies now dismisses the need to conduct deeper, followed by shallower dives. That recommendation was instituted because of a lack of research into dive series and decompression. Further, more modern, research indicates that the order of deeper/shallower dives is immaterial, providing each specific dive is properly decompressed.

As a matter of (un-scientific) precaution, many agencies still recommend that subsequent 'deeper' dives are no more than 10m/33ft deeper than previous dives.

 

[Necklinsberg]

Isn't every shore dive by definition a reverse profile dive (shallow --> deep --> shallow)?
Back when the padi rdp (and other companies' planners) were developed, where the studies based shore dives or boat dives or a mixture of both?

 

[boulderjohn]

Isn't every shore dive by definition a reverse profile dive (shallow --> deep --> shallow)?
Back when the padi rdp (and other companies' planners) were developed, where the studies based shore dives or boat dives or a mixture of both?

We are getting confused about the terms. The PADI RDP mentions that in a series of dives, the deeper dive should be done first. That has been challenged in the last decade, and the consensus now is that if your surface interval allows a second dive that is deeper than the first, it is OK.

On a single dive, whether it is done from shore or a boat, you always start at the surface and head on down. That cannot be avoided. During that dive, you should endeavor to get to the deepest point early in the dive, and either stay at that depth or get progressively shallower. Although it is possible to do the opposite--stay shallow for most of the dive and then get deeper before your ultimate ascent--and be OK, that is really not the best way to do it.

 

[Kharon]

You are confused.

Not according to the SDI "Deeper Sport Diving and Dive Computers" training manual page 88.

 

[WetLens]

Back in 1990, we were on a 10-day dive trip aboard the Reef Explorer II. According to our divemaster, the Queensland rules of diving dictated that each subsequent dive be shallower during a day of diving. Further, we were limited to 4 dives per day - including the night dive. Quite a few on the trip were instructors (mostly YMCA and NAUI) and could not believe these limitations as there was no real basis for the rules. Yes, we taught and recommended deeper dives first and deeper portions of dives first, but those recommendations were based on maximizing bottom time. What this rule did was to promote diving deeper than needed on early dives just to open the window should diving deeper on subsequent dives be advantageous. In actual practice, we simply lied when we climbed on board - first dive was always reported as 100' regardless of how deep we actually went. Ridiculous rule forcing ridiculous behavior.

Imagine my surprise earlier this year when the same rule was being enforced on Caribbean Explorer II in the Turks & Caicos.

 

[DevonDiver]

Not according to the SDI "Deeper Sport Diving and Dive Computers" training manual page 88.

Publisher: Scuba Diving International/International Training, Inc (1 Jan 2001)

I'll refer you back to my earlier comment: "That recommendation was instituted because of a lack of research into dive series and decompression. Further, more modern, research indicates that the order of deeper/shallower dives is immaterial,.."

Care to quote anything else out of date?

 

[knotical]

Ah, terminology bites us again.

As DD suggests, I too would like the term “reverse profile” to apply to the profile of a single dive in which the diver does the deeper portion of the dive toward the end. BUT:

The Workshop adopted the definition that a reverse
dive profile was either two dives performed within 12 hours
in which the second dive is deeper than the first; or the
performance of a single dive in which the latter portion of
the dive is deeper than the earlier portion.

from: http://archive.rubicon-foundation.o...e/123456789/7677/SPUMS_V32N2_9.pdf?sequence=1

It’s just another one of those somewhat ambiguous terms we use. Another example is “two-tank dive”.

Welcome to my club - I'm often confused too.

 

[Kharon]

... more modern, research indicates that the order of deeper/shallower dives is immaterial,.."

Care to quote anything else out of date?

Care to provide references to scientific studies so that your statements can be verified?

 

[WetLens]

Proceedings of Reverse Dive Profiles Workshop.

"FINDINGS: 1. Historically neither the U.S. Navy nor the commercial sector have prohibited reverse dive profiles. 2. Reverse dive profiles are being performed in recreational, scientific, commercial, and military diving. 3. The prohibition of reverse dive profiles by recreational training organizations cannot be traced to any definite diving experience that indicates and increased risk of DCS. 4. No convincing evidence was presented that reverse dive profiles within the no-decompression limits lead to a measurable increase in the risk of DCS. CONCLUSIONS: We find no reason for the diving communities to prohibit reverse dive profiles for no-decompression dives less than 40 msw (130 fsw) and depth differentials less than 12 msw (40 fsw)."

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Also read:

http://www.blueplanetdivers.org/archives/2006/10/the_controvesy.php
October 16, 2006 [h=3]Controversial Reverse Dive Profiles[/h]