Reverse Profile Diving

[scubawheels]

I've heard some new thinking that reverse profile diving is not as dangerous as once thought. What are the thoughts of the ScubaBoard community in regards to reverse profile diving?

The reason for my question is this....Recently on a trip to the Straits of Mackinaw, we planned to complete two dives on two wrecks. The deck of the first, the Stalker, is at about 85 feet. The deck of the second wreck, the William Young, is around 105 feet. I felt no ill effects after the dives, other than disappointment because my second dive was very short; the William Young is one of the best wrecks in Mackinaw.

 

[vjanelle]

From a nitrogen loading standpoint it's not optimal, but people generally agree that it's not dangerous, except for some bubble model researchers who say it's ok except if the second dive is a certain range deeper than the first.

 

[Bubbletrubble]

Read this DAN webpage.

Understand that there is the issue of safety with respect to DCS risk (so long as NDLs are not violated) and the separate issue of "best use of dive time." The prevailing opinion, I believe, is that for recreational dives with less than a 36 fsw depth differential, reverse dive profiles do not present a significant increase in DCS risk (vs. "traditional" forward dive profiles).

I recommend doing your own analysis of the scientific evidence. A nice tool to help you do this is the Rubicon Foundation's publication archive. Search for "reverse profiles."

Relatively recent research on the topic yields the following:
McInnis et al. believe that forward dive profiles are safer than reverse profiles based on a study of guinea pigs.
I like Jan Risberg's take on the subject.

 

[AndyNZ]

I recommend doing your own analysis of the scientific evidence. A nice tool to help you do this is the Rubicon Foundation's publication archive. Search for "reverse profiles."

+1


The Rubicon repository is your friend, a great source of knowledge. The 400+ pages in the proceedings of the 2000 Reverse Profiles Workshop are well worth reading.

The history of the "no reverse profiles" [-]rule[/-] guideline is also an interesting thing to look in to and certainly opens your eyes to the reasons why such a [-]rule[/-] guideline was introduced.

Having spoken to attendees at the 2000 workshop, the recommendation that came out of it was nearly "Reverse profiles? No problem!" but that was caveatted into the recommendation because some proponents of particular decompression models felt that under some circumstances the theory indicated that there might be a risk.

Of course, it's worth remembering that decompression "theory" isn't really theory at all - it's conjecture, with some degree of empirical evidence to support it.

Read the material, make your own choice!

 

[TMHeimer]

While it seems to make sense that it's your total nitrogen loading on the 2 dives that counts (& SI, of course). Thus a reverse profile should make no difference. But an instructor explained to me the reasoning that it is more dangerous (can't remember the specifics), and what he said seemed to make sense.

 

[Blackwood]

While it seems to make sense that it's your total nitrogen loading on the 2 dives that counts (& SI, of course). Thus a reverse profile should make no difference. But an instructor explained to me the reasoning that it is more dangerous (can't remember the specifics), and what he said seemed to make sense.

[-]It's less in-water deco, plain as day.

As long as you prepare for it, there's nothing inherently wrong with shallow before deep. Sometimes the environment dictates.[/-]

edit: guess I should read the entire OP before responding.

Regarding a second dive deeper than the first, some people think that's better, as any bubbles formed on the first dive may potentially be crushed and then exhaled. Really this is all theory (or, as Andy said: conjecture). Even if one way were demonstrably better from a decompression standpoint, I really doubt it would manifest itself in a 20' difference, particularly on sub-NDL profiles.

 

[Rhone Man]

Bubbletrubble beat me to it, but I think the DAN article largely concluded that there was nothing to conclude that reverse profiling was intrinsically more dangerous, but they did up giving a slightly water down conclusion. Old habits really do die hard.

 

[knotical]

To me, the biggest issue with "reverse profiles" (deeper dive second) is that you get less total dive time, or need longer surface intervals. Run a few examples with your choice of model.

 

[Hatul]

To me, the biggest issue with "reverse profiles" (deeper dive second) is that you get less total dive time, or need longer surface intervals. Run a few examples with your choice of model.

That's also my understanding of the main problem with reverse profile, it's less efficient in terms of dive time.

Adam

 

[vjanelle]

The other issue is that people used to espouse them as being "dangerous", but no one could figure out who exactly said this to begin with.