Reverse dive profiles

[Don Burke]

ScubaJeep once bubbled... Well, if you put all of your faith into the dive tables then you are safer with a normal profile. My question is whether those tables deserve that amount of trust.

Is a normal dive profile easier on your body than a reversed?

The answer to the first question is that all of the algorithms come up with lower tissue loading when the deep dive is first. While different tables and computer programs differ in how much lower, they are all lower.

I don't understand what you are getting at with the "all of your faith" statement. All algorithms are approximations and every diver should know that. Normal profiles give a better safety factor. If you are suggesting that the tables are reversed, you'll find few, if any, to agree with you.

Your alternative would be to ignore all guidance? I suspect not.

Lower tissue loading is easier on the body, so the answer to the second question is "yes".

 

[Charlie99]

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.

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.
....
From a decompression point of view, we have seen that repetitive diving makes no difference, so we ignore the first dive in calculating the second. The only trick is that the second dive should be deeper than or equal to the first, and you can not bounce dive after a dive of any kind.

Trivia question for the day: Who wrote the above?


The original source can be found at http://tinyurl.com/rnuq

(emphasis is mine)

 

[Waterborne]

Trivia question for the day: Who wrote the above?
(emphasis is mine)

None other than the WKPP's own GI3 from his article on repetitive diving. To be followed by his artice on why they do not bounce dive in the WKPP.

 

[cornfed]

SCUBAMedicBill once bubbled...
Using ScubaJeeps dive plan, is shows, as shown by Don, that doing the deep dive first and the shallow last leaves you with a bigger span between ABT and NDL (43min vs 11 min). There's the SAFETY. On this dive plan, it doesn't make too much of a difference, but it could on other dives plans.

It's no more or less safe then pushing the NDLs on a set of "regular" dives.

Why do people get so hung up on the "reveresed" part?

 

[Saturation]

SCORE ResQ once bubbled...

None other than the WKPP's own GI3 from his article on repetitive diving. To be followed by his artice on why they do not bounce dive in the WKPP.

Most of what GI3 says makes sense, in fact, he was writing about a VPM schedule with some tweaks of his own.

However, for the meantime, ignore his comments about what he can do and what others cannot. Its a long story.

However, that repetitive article is voodoo if not understood in context.

All repetitive dives must take into account residual nitrogen, but the time needed to offgas on a recreational table versus a decompression table are not similar. A deco schedule may have less residual N2 on surfacing because of the 02 used for decompression and depends on how much He is used in trimix, but its not zero. In a heliox dive, its very possible there is no remaining inert gas post dive and one could 'dive' again and ignore residual inert gas time.

A recreational reverse profile is allowed with a maximum differential between dives of 40 feet. This minimizes the effects of squeezing microbubbles into the arterial circulation. Wienke also recently suggests that 70' differentials are considered in dives past 100'.

 

[Don Burke]

SCORE ResQ once bubbled... None other than the WKPP's own GI3 from his article on repetitive diving. To be followed by his artice on why they do not bounce dive in the WKPP.

The reason for reversing the profile is stated in the article. CNS oxygen problems.

Unless it is being contended that oxtox is an issue on a 20 minute dive to 70 feet followed by a 20 minute dive to 50 feet, I'd say this is pretty far out of context.

I don't imagine that Jeep would be up for the deco that the WKPP divers do either.

 

[ScubaJeep]

Don Burke once bubbled...
I don't imagine that Jeep would be up for the deco that the WKPP divers do either.

Not at this point in my diving career.

So, to sum it up: Normal dive profiles leave better margins for safety. Reverse dive profiles are possible, but have limits, and must be strictly planned as to not exceed NDLs. Your dive tables give you reliable information whether your profile is normal or reversed. And finally, George Irvine of WKPP is pretty hard core.

 

[Waterborne]

So, to sum it up: Normal dive profiles leave better margins for safety. Reverse dive profiles are possible, but have limits, and must be strictly planned as to not exceed NDLs. Your dive tables give you reliable information whether your profile is normal or reversed. And finally, George Irvine of WKPP is pretty hard core

Yeah ScubaJeep, I'd say that sums it up pretty well.

FYI, the bit about bounce diving was only intended as a joke, hence the smiley. It is the next article in the list on the site. Probably a poorly timed joke but, a joke nonetheless.

 

[cornfed]

ScubaJeep once bubbled...

Reverse dive profiles are possible, but have limits, and must be strictly planned as to not exceed NDLs.

This is basic dive planning.

"Regular" profiles have no inherent safety factor over reverse profiles. If you plan your dives to push the NDLs you're decreasing safety, it doesn't mater if they're forward or backward.

 

[pipedope]

Was done (and is done) with the idea that the following, shallower dive (or dives) act somewhat as decompression for the first deep dive.

This does, sort of work diving air.

If you are doing dives that have significant deco obligations then air should probably not be a breathing gas except at the surface.