Reverse Profiles - do we have it backwards?
The core issue is that the conclusions of the Workshop on Reverse Profiles at the Smithsonian Institute did not recommend a departure from the "deepest dive first"; the findings merely stated that there was no evidence to show it was specifically detrimental if the dives were both no-decompression dives, shallower than 40 meters, and the depth differential between the dives was less than 12 meters.
In practice, though, to meet this proviso one would need to consider dives of 12 to 30 meters (as no-deco dives on 40 meters are impractical). DAN has also commented on this in the past [Click here].
An area of concern, though, is the rather common practice of using dive computers to perform decompression dives, but to avoid the 'need' for a stop by spending a significant portion of the dive in shallower water until the stop eventually disappears - pseudo-no-decompression diving. The Workshop did not examine the impact of reversing profiles of this nature.
In simpler words then, if diving is performed within the no-d limits (and less than 40 meters), and the different dives are done within a maximum difference of 12 meters, the current evidence does not show any demonstrable increase in risk of DCI. This still stands. The question divers need to ask is whether the effect of the residual nitrogen penalty on the second deeper dive makes sense.
Still worth doing the deepest dive first and, if possible, always do a safety stop at the end of every dive.
Doing the shallower dive first will reduce one's No Deco second deeper dive time quite substantially, where as doing the deeper dive first is not as inhibiting on the shallower dive second dive, and total bottom time is therefore increased. Safety stops are always time well spent, however the tendency to bolt for the surface once completed is a no no, a full minute to surface is ideal.