do your shallowest dives first?

[sunnydiver]

I got confused,
i read from:
http://www.divetekadventures.com/Technical_BubbleFormationElemination.htm

that i should do first my shallowest dives. Padi teached to do first the deepest dives. Did i miss something?
Do they (DIR) handle other kind of rulles?

 

[ScoobyPat]

I try to stay well withing the NDL and do my deepest dive first. I guess you can do it the other way around, as long as you stay within the NDL, but I am not an expert or deco god. ;-)

 

[Don Burke]

Hi Sunny,

That article by George Irvine was taken out of context.

He is assuming that all of the dives you are going to do are staged decompression dives and oxygen toxicity is going to be an issue.

For no-stop diving you'll get more bottom time for a given amount of risk by making the deep dive first.

 

[Kendall Raine]

Don;

I'm not sure toxicity is the context, or at least the whole context. I think George is primarily alluding to microbubble excitation. Deepest dive first sets up a larger bed of microbubbles into which inert gas can diffuse from the second dive. This interpretation jibes with his no bounce dives-"give yourself a PFO"-observations. Perhaps Bruce or Mike can illuminate.

Also, I seem to recall DAN backing off the deepest dive first dictum some time back. I think they said there was no physiological advantage provided you did the correct profile for each. Maybe someone has a better memory or can locate a cite.

 

[cyklon_300]

http://www.umich.edu/~oseh/reverse.pdf

 

[SDAnderson]

Reverse profiles, within limits, should not cause problems for normal recreational divers.

In October, 1999, a workshop was held to review whether reverse dive profiles are cause for increased risk. The workshop was organized by Michael Lang, Diving Officer and head of the Smithsonian Institution's Scientific Diving Program and Charles Lehner of the University of Wisconsin, chairman of the Underwater Hyperbaric Medical Society Workshop Committee. The workshop was supported (and attended) by a veritable Who's Who of the diving and hyperbaric medical world.

The findings of the workshop were:

• Historically neither the US 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 organisations cannot be traced to any definite diving experience that indicates an increased risk of DCS.
• No convincing evidence was presented that reverse dive profiles within the no-decompression limits lead to a measurable increase in the risk of DCS.

The conclusion:

The workshop finds 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).

Steven

 

[Kendall Raine]

That's the one I was thinking of. I think this was reported in Alert Diver.

Thanks.

 

[Don Burke]

The item off the University of Michigan site stated that reverse profiles are involved in 28.8% of the cases where the profile is known. Of course that number means little unless we know the precentage of divers doing reverse profiles.

I have a little trouble buying into the prospect that all of the cattle boats out there aren't enough to push the percentage of dives done on "normal" profiles well above 71.2%. I can't prove it, so I won't argue it.

Of course you can dive reverse profiles. Every algorithm I have seen comes up with less bottom time for the reverse profile of the same two dives. If you have one where a 100 foot dive and a 50 foot dive can be done in either order with no bottom time penalty, I'd like to see it.

I shouldn't have mentioned oxygen. I'll dig out the link where George talks about it and post it later.

 

[Don Burke]

Here's the article about diving reversed profiles to minimze oxygen problems:

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

It has little to do with the case at hand, but since I brought it up, I wanted to close the loop.

 

[sunnydiver]

I guess that this topic is beyond my level as a new diver.
I will have to read more about it to understand it better for what he (George Irvine) was talking about.
But the point for what he was making, didn't sounds logical for recreational divers. Beacuse as so far as i have read and been told, it seems much more far logical to make first your deep dives.
In the otherway arround you, are compressing again your nitrogen bubbles...