Reverse Profile Diving

[craracer]

I recall reading somewhere that the recommendation to do forward profiles began with PADI back in 1972. The recommendation eventually evolved into a steadfast rule, which other organizations latched onto.

The original PADI manual had no supporting evidence to back the forward profile rule.

 

[jtivat]

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.

I would have no issue doing those dives in that order. Yes the William Young is very cool but the EberWard is my favorite in Mackinac.

 

[drbill]

I have dived reverse profiles for many years (although not on every dive of course). My dive profiles are a function of the specific sequence of dive sites and critters I can expect at each, since my "porpoise" in diving is to film critters to help educate non-divers about what there is "down under." Often times each dive's profile sends me into deco if we're diving certain sites around Catalina as the depth drops off quickly.

However, I tend to be very cautious about my deco times. I often triple any required deco, or try to double it if it is a long one. I'm an old geezer so I prefer to be more conservative on that than some are (meaning those who accept the required deco).

 

[scubawheels]

Thanks to everybody that has posted so far, I appreciate the info!

I wondered if the difference in depth would be a factor, and if only 20 feet would be enough to make the dives "dangerous." I doubted it. The dive time was a factor, my dive on the Young was very short, also I think my computer is extra conservative and didn't like my profiles.

jtivat - The Ward is great, I've done it a couple times. My favorite part of that dive is going to the bottom, looking up, and getting a great sense of the size of that ship. Especially for a wooden ship in that time period. The Cedarville is also great in terms of size, but I prefer the old wooden ships.

 

[jtivat]

The dive time was a factor, my dive on the Young was very short, also I think my computer is extra conservative and didn't like my profiles.

Take a basic deco course and you can start spending 30 minutes on wrecks like this with 45 minute runtimes. In fact the first dive I did on the Eberward many years ago was like 5 minutes and I decided that was crazy. I took Advanced Nitrox and Deep then went back and did 30 minutes on her it was awesome.

 

[scubawheels]

I hear ya, a Nitrox class is on my schedule for next month. My other two days of diving in Mackinaw that weekend consisted of 25-35 minute dives, not bad, I start getting cold in my 7mm by that time anyway. However, basic tech diving will come down the road I'm sure.

 

[Jim Lapenta]

I'd be curious as to how many instructors cover reverse profile dives in any detail to show students what they are up against as it pertains to run times, surface intervals, and how if you are not careful it is easy to run into deco on a dive you'd never expect to. As Knotical said run the numbers on whatever tables you like. Do shallow first and then deeper. I've been doing this with my OW classes since last year. Just to show them how the tables work.

 

[Damselfish]

I'd be curious as to how many instructors cover reverse profile dives in any detail to show students what they are up against as it pertains to run times, surface intervals, and how if you are not careful it is easy to run into deco on a dive you'd never expect to.

we actually did cover that in OW - PADI even - compared the same dives different order to show how doing the deeper last came out less conservative - at least when following tables.

 

[boulderjohn]

I recall reading somewhere that the recommendation to do forward profiles began with PADI back in 1972. The recommendation eventually evolved into a steadfast rule, which other organizations latched onto.

The original PADI manual had no supporting evidence to back the forward profile rule.

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.

The 1972 handbook suggested doing the deepest diver first. I have not read the exact language, but my understanding is that the reason for the suggestion was not clear, and PADI looking back at it could not tell why, either. My guess is that it was not because of a DCS-linked danger but rather for the reason knotical states: using any tables, you will be able to get a longer second dive and/or less required surface interval if you do the deepest dive first.

If, on the other hand, you have had enough surface interval to do the dive you want to do on the second dive, there should be no problem if it is deeper.

 

[boulderjohn]

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.

The path this suggestion followed takes place in all walks of life. A certain concept is initiated for reasons that are not always clear. Often it is because of some sort of equipment limitation, etc. As time goes by, the concept becomes thoroughly ingrained, and no one knows the real reason for it. Pressed to explain why they follow this customary practice, people often invent reasons, usually with the best of intentions. ("I think this must be the reason.") Those reasons get repeated from one person to another, and, like the famous telephone game, take on new twists.

I remember well when the reverse profile conference findings were released. I was not yet a professional. I mentioned reading about it to someone who was a DM. He got really huffy and said it was madness. He explained all the reasons for the reverse profile prohibition. He mentioned studies he had read himself. He acted as if he knew more about it than the authorities who had been at the conference. I listened intently, and it made sense.

Shortly after that I began working on my own DM and studied decompression theory. I realized pretty quickly that everything he had told me was pure BS. He really didn't understand deco theory himself, and the studies he alluded to, the ones he himself had read, did not exist.