DAN 2001: No Basis for Diving Deep First
In November 1999, a group of Italian dive clubs and organizations invited Dr, Bennett to speak to an international meeting in Padova, near Venice. More than 500 divers attended. His topic was “Decompression Today: Algorithms and the Importance of Rate of Ascent,” emphasizing again that we need to keep our ascents slow.
Those in attendance were well-informed and asked lots of questions about ascent rates, children and diving, nitrox, rebreathers and reverse dive profiles.
DAN held similar workshops around the United States, that they called “Divers Days.” Usually on a Saturday, these events were often held near a recompression facility so you could visit the chamber and meet DAN staff and other physicians, scientists and divers to talk about dive safety.
In October, 2000, DAN also co-sponsored and helped fund another workshop, “Reverse Dive Profiles,” at the Smithsonian Institution in Washington, D.C. DAN Board member Michael Lang and Charles Lehner, a very fine researcher in decompression and underwater physiology from the University of Michigan, co-chaired that workshop. In addition, anybody and everybody in diving decompression theory was present – more than 50, in fact.
What is a “reverse profile”? It can be defined as two dives performed within 12 hours, in which the second dive is deeper than the first; or a single dive in which the latter portion of the dive is deeper than the earlier portion.
Historically, neither the United States Navy nor the commercial diving sector has prohibited reverse dive profiles, which are being performed in the recreational and scientific diving communities.
The workshop concluded, after 289 pages of presentations and discussion: “…no convincing evidence was presented that reverse dive profiles within the no-decompression limits lead to a measurable increase in the risk of decompression sickness;” and “We find no reason for the diving communities to prohibit reverse dive profiles for no-decompression dives less than 130 feet / 40.6 meters and depth differentials less than 40 feet / 12.5 meters.”
Thus, it has now been established, based on operational and theoretical data from more than 50 experts, that there is no PHYSIOLOGICAL basis for diving deep first. This means that there is, therefore, no evidence available to suggest an increased risk of DCS when doing a reverse dive profile versus diving deepest first.
Remember, however, to keep your ascent rate slow, especially from the 15- to 20-foot (4.5- to 6- meter) safety stop.