Many times, in my professional activity (mostly in the role of dive guide), I witness the inexplicable behavior of divers who, after a perfect safety stop at 5 meters performed in very good buoyancy, rapidly swim to the surface or even worse just inflate the BCD and pop up uncontrolled.
These divers are probably convinced that after the safety stop there is no more risk and it’s possible to return rapidly to the surface and thus to the boat… Well this could not be more wrong!
If we consider the Workman critical ratio 1,58:1, we can easily understand that a rapid ascent from 5 - 6 meters is at the very limit of this value! Moreover, the most modern VPN and RGBM decompression models imply the constant presence of bubbles in the body tissues, and in a previous article we learned that a full washout (off-gasing) of bubbles relevant for DCS only occurs in the 12 - 24 hours following the dive. So, given the presence of bubbles in the tissues while we still are underwater, the sudden pressure decrease caused by a rapid ascent from 5 meters could trigger the production and growth of bubbles potentially relevant for DCS.
Furthermore, a rapid ascent from 5 meters is not only relevant in terms of DCS, but also with reference to pulmonary injuries and barotrauma, such as reverse squeeze.
In particular we shall always keep in mind that, if we surface holding the breath with full lungs, a depth change of only 1,2 meters is sufficient to cause lungs over-expansion!
Finally, considering, the massive pressure change in this delicate phase, it is recommendable to choose an ascent speed even slower than the 9 m/s recommended by many training agencies. Considering an ascent rate of 6 m/s, we should take at least one minute to surface from 5 meters!
No need to say that in this phase, perfect buoyancy is the most important skill to be mastered, so keep training and, if necessary, join dedicated buoyancy courses.
No comments:
Post a Comment