INFO SHEETS > THE ASCENT PHASE
Ascent rate: a whole story
Ascent speed is essential to preventing the risk of desaturation accidents (ADD). Yet his determination has often been made in an arbitrary fashion throughout the history of diving.
A slow and uniform ascent
In 1878, Paul Bert, who highlighted the role of nitrogen in desaturation accidents, proposed a “sufficiently slowed down” desaturation, of the order of 0.5 m per minute, regardless of the depth reached and the time. Diving. In this, it joins the “slow and uniform ascent at 0.5 m / min” recommended by Heller, Mager and von Schrötter.
For its part, Denayrouze offers 1 m / min.
“While the group of divers among whom the accidents occurred reached considerable depths of 45 to 54 meters […], Mr. Denayrouze, with a caution which does him honor, had given the order not to exceed 35 meters, not to stay more than 2 hours 30 minutes, per diver and per day, and finally to go up very slowly, putting one minute per meter of depth. "M. Leroy de Méricourt, Considerations on the hygiene of sponge fishermen, 1869.
A faster ascent but with stages
In 1908, J.-S. Haldane, creates the first dive tables and the ascent in stages, depending on the dive time and the depth reached, with the recommendation of an ascent rate of around 10 m / min:
- 6 to 8 m / min up to 20 m deep. max. ;
- 10 m / min for dives between 40 and 20 m deep. max. ;
- 10 to 14 m / min for dives between 60 and 40 m deep. max.
Until 1957, the ascent rate thus remained around 8 to 10 m / min.
The divers and the frogmen
From 1958, a controversy arose between the frogmen of the US-Navy commanded by Francis Douglas Fane (1909-2002) and heavy-footed divers, deep-sea divers. The former require a speed of 30 m / min while the latter remain stuck on an ascent rate of 3 to 6 m / min.
Bitter discussions lead to a purely arbitrary compromise. It was decided to define a median value:
(30 + 6) / 2 = 18
This is the ascent speed of the US-Navy tables, in effect from 1958 to 1993. This speed is also used by the RDP-PADI tables (which are only an adaptation of the US-Navy tables) and the MN- tables. 90 adopt a similar value: 17 m / min (now 15 to 17 m / min).
Modern times: 10 m / min
From the workshop Biomechanics of Safe Ascents from 1990, the question is no longer debated: the theoretical speed of 10 m / min (9 to 12 m / min in practice) is recognized as the good ascent speed in recreational diving, making it possible to limit the level of bubbles as much as possible (detection by Doppler effect).
The US-Navy tables moved at this speed in 1993 (US-Navy Manual Revision 3 of February 15, 1993).
Most of the computers on the market have followed suit.
© Extract fromPleasure Diving booksby Alain Foret at Editions GAP.
Any reproduction prohibited on any medium whatsoever without the written consent of the publisher and the author.