Reverse profiles

Question:
I’m Instructor and I have a very BIG question for your Physiologic and Decompression theory experts.
I want to make two dives,
First one at 09H30 AM to 12 meters for 50 minutes and after a 2H40 minutes, a second at 01H00 PM (the same day, to really don’t confuse you in my question) to 28 meters 15 minutes following by a multilevel 16 meters for 10 minutes and 12 meters for 15 minutes.
Now the big questions, is it physiologically safe for me.
I know already that the recommendation is to dive deeper first and shallower on repetitive dives. I know, as a diving Instructor, all the recommendations and the basic of physiology and decompression theory but I want to know more about this kind of reverse profile.
Nobody is able to explain me why is it dangerous or why is it not, on the physiological side. That why I write you now, DAN, the professional on that.

Answer:
There is no "physiological" danger or significant alteration related to reverse profiles that has been scientifically proven. That is, the physiology of the uptake and desaturation of inert gas is not changed by a reverse profile.
Obviously, however, a deeper dive following a shallow and possibly long one, would impose on the already supersaturated tissues a further significant saturation, in a short time, since the driving force for the uptake of inert gas is stronger with the increase of depth and inert gas partial pressure.
The end result would be a significant inert gas supersaturation of the tissues, rapidly approaching the No-D limit or reaching times which may make Decompression Stops necessary. This can be easily seen by computing such dives on tables or scrolling the simulation on a dive computer.
It is known, also from our recent studies, that the probability of high degree gas bubbles and of decompression illness is linearly proportional to tissue nitrogen partial pressure and depth.
A symposium on reverse dive profiles was held in October 1999 in Washington DC, at the Smithsonian Institute, co-sponsored by DAN, DEMA and others. The Reason was to substantiate with scientifically sound findings the current statement by many Training Agencies that reverse dive profiles are not recommended due to an increased risk of DCI. The conclusions of the workshop are the following:
"The Findings
1)Historically neither the US Navy nor the commercial sector have prohibited reverse dive profiles
2)Reverse dive profiles are being performed in recreational, scientific, commercial and military diving
3)The prohibition of reverse dive profiles by reacreational training organizations cannot be traced to any definite experience that indicates and increased risk of DCS
4)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 Conclusions
We find no reason for the diving community to prohibit reverse dive profiles for no-decompression dives less than 40 msw (130 fsw) and depth differentials less than 12 msw(40fsw)."

In simpler words, if diving is performed within the no-d limits 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.