Multi -dives

[MATTBIN]

Quote
"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."

Discuss!

Matt

[Andrew H]

Doesn't appear to make sense. GI3?

Andrew

[Narked@50]

Is this some kind of trick question??

If it is, you've got me, cause I think it's BO**OCKS

James

[Neil M]

one phrase.... "Off gassing"???

[jlwarlow]

Where was this quote from?

[MATTBIN]

GI3 indeed, is he correct, if not why not.
Matt

[Andrew H]

Originally Posted by MATTBIN

GI3 indeed, is he correct, if not why not.
Matt

That was a guess based on the nonsense feeling of the quote. I have since located it on WKPP. I must make the effort to read all that. Can someone lend me GI3 for dummies or will I have to translate it for myself?
Since they're not dropping like flies, they might well be into something. Without having read it, I suspect that the idea is that the greater deco commitment from the second deeper dive will override any residual from the first dive. You would need to be very confident of your offgassing in this case. Also it might well be specific to accelerated deco using DIR mixes, and probably for longer runtimes as well. Bounce dives would give shorter deco times and therefore not allow for full off gassing.

Or something.

I'll try reading the deco section at WKPP and see if I can make any sense of it.

Andrew

[adam]

Before you all reject it out of hand.....why not turn this around?

Why do we need to take surface intervals into account, and why should your first dive be the deepest? Please discuss!

Because the book says so is not a valid answer! Remember that all these ideas are just based on models-it may be that none of them are actually anything like what is actually happening during and after a dive. All we are trying to do is predict some outcomes!

The big hint is that contrary to every dissolved gas model out there, bubbles do form after every dive. There is no such thing as a bubble free dive-just degrees of how much bubbling actually occurred.

In which case, the aim of deco is to prevent these bubbles from being harmful. If you deco correctly, then there is simply no need to account for surface interval-you have off gased all you need to (or you won't be able to surface without bending)!

If you then dive to a shallower depth, any bubbles that are left (and there will be some harmless ones) can be recompressed, and can end up passing through the venous circulation onto the arterial side-ready to cause a problem during that ascent. If each dive is deeper than the previous, and you deco out from each one properly (i.e. no "bounce diving") then when you recompress bubbles, they will be dealt with.

These concepts will not work within dissolved gas models, so please don't compare/contrast anything within them to this. For more info on these models see And's excellent post on Buhlman etc, and some of the stuff on the 02 window. At then end of the day, all we can do is make a personal choice of which model to use.

Hope that helps

Adam

[alunharford]

Originally Posted by MATTBIN

Quote
"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."

Discuss!

Matt

From the NDC Diving Incidents Report 2003, 20% of incidents involving DCI were thought to have repetitive diving as a contributing factor.

[Dave Crampton]

Hi I've just been simulating dives on my Suunto software, and I have to say I think just because your into a stop dive, you can't just keep diving stop dives (deco) as each were as bad as the last. Recall that there are 16 compartments in the bhulman ZHL-16x model. the first compartment has a short time with the last having a very long (couldn't find the actual values online) time. So effectively unless the first couple, in the series of dives, were deep, you'd still be on gassing those longest comparments during your consecutive dives, as they would not nessessarly be saturated after the first dive. Yes the short compartments would saturate and then off gas on your deco penalty, but the longest compartments would be on gassing (with short off gas phases) more throughout the series of your dives. Eventually (depending on the depths you were diving to and the dive times), your longest compartments would saturate, yeilding considerable deco penalties. I have a feeling the dive profiles would have to be done by hand/computer as the dive computer might lock you out after an extending series of dives. Then there is the logistics of taking enough gas on your dives (increasing as you dive) to cope with the lengthening deco penalty you were incuring.

Just a novices thinking behind this.

Dave C