| 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  |