No matter the subject, certitudes are rare in the scientific litterature. It is particularly the case with diving, some concepts still cause debate these days. Nevertheless, multiple studies led to knowledge that few scientists dare speak against:
• For diving with air, deep stops are considered to be dangerous and should be avoided.
• Multiple and repeating dives show particular dangerousness and should be computed with a specific and adequate procedure.
Here is what Albert A. Bühlmann wrote :
Experimental dives and statistics (DAN, BSAC) confirm a higher risk of decompression sickness for repetitive dives. Microbubbles in the venous blood obstructing a part of the lung capillaries produce ventilation-perfusion trouble, a right-left shunt well known in lung physiology.
Source : Albert A. Bühlmann, Behavior of dive computer algorithms in repetitive dives : experience and needed modifications, in Hamilton R.W. edition, UHMS Workshop 81, 6-1-1994, Undersea and Hyperbaric Medical Society.