Hopefully, I did not miss it.  Did anybody actually get bent freediving or
is this all theory?

Lee

----- Original Message -----
From: "John Nitrox" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, April 14, 2004 12:30 PM
Subject: Re: [SCUBA-SE] An u/w Segway?


At 05:44 AM 4/14/2004, Lee Bell wrote:
>"John Nitrox" wrote:
>
> > http://www.aidabrasil.com.br/artigo010.htm
>
>I get a "Page Can Not Be Displayed" message.


         This seems to be happening to a lot of people so with an apology
to everyone for grabbing so much band width, here's the text of the URL.

>SHORT SUMMARY
>
>
>Decompression sickness and freediving
>
>
>
>
>
>Schaeffer (1955)1 verified several time the existence of silent bubbles in
>blood after one fast ascent from 30 meters (non pathological).
>Conditions for the appearance of silent bubbles : quick decompression ;
>ration depth pressure/surface pressure>3 ; important muscular exercice
>during the ascent.
>Paulev (1965)2 showed that decompression accidents like Taravana can
>arrived after repeatitive dives at high frequency, even if the depth is
>not 30m.
>Below, (left part of the picture) example of another experiment realized
>by Paulev in 1969 to demonstrate that for a tissu which period is
>40minutes, the critical value of N2 tension is reached after 16 dives at
>30meters (dive time 2', rest at the surface 1'). The right part of the
>picture demonstrate the same fact but first, the freediver stays 30' in an
>hyperbaric chamber and after (« A » curve) realize 6 dive to 30m with the
>following frequency : 2' dive time, 1' surface rest. « B » curve is for
>surface rest = 5' ; « C » curve is for surface rest = 10'
>
>
>Lanphier (1965)3 is the first to propose by a calcul a conversion factor
>to adapt the diving  decompression tables to freediving.
>The « K » factor is the ratio between surface time and dive time. If K =
>2, it means that the dive is 1' and the surface rest is 2'. Ascent and
>descent are considered to be instataneous.
>He proposed after his study the picture below (calculated for a tissu : T
>= 20'). The tissu taken into consideration is a good compromise to reflect
>the whole body behavior. (an intense exercice increase the N2 gradiant
>between tissus and alveolus and lead to under estimate the equivalent
>depth : on another side, ascent and descent being not instantaneous this
>procedure lead to over estimate the equivalent depth). If you know the
>depth you dive, you use the picture below to determine the max duration of
>the training.
>
>
>For example 2' rest, 2' dive means K = 1. If you go each time at 30
>meters, after a training of 60' we have to take a classic decompression
>table and consider you have dived 60' at 50% of 30m.
>BUT, decompression tables are made for a speed ascent = 10 to 15
>meters/minute.
>
>The picture below illustrate the 2 different curves we have to take into
>consideration (safety curve). We can see of course that an omportant speed
>ascent increase the risk.
>
>
>SO, Lanphier (1965) proposed a picture which combined the two above
>picture and obtain the picture below. Knowing K and depth, we read the max
>possible training time.
>
>
>
>
>
>Example : I dive in 40 meters, K = 2, max training time is 120 minutes.
>
>
>Doctor Heran (1991) and Grandjean and coll (1995) worked also in France on
>this problem.
>
>Heran proposed  in 1990 a table in which it was possible to determine the
>max dive number in one hour we should realize, knowing depth, dive time
>and duration of the training. Picture below :
>
>
>Example : training duration : 4 hours, dive depth : 30m, 12 dive of 2' per
>hour : risk of decompression sickness is real.
>
>TRAINING ADVICES
>
>Waiting deep freediving tables (we should find, if they exist, such «
>Heran's tables » for depth between 40 to 80 meters), we could give the
>following general advices for trainings :
>
>-         Short trainings are better
>-         Drink water during the training (deshydratation increase
>decompression accidents)
>-         Be carrefull with hypothermy (cold help the N2 saturation)
>-         Don't practice with fast ascent (In No limit, let the balloon go
>away at the end of the ascent while you finish by pulling the rope with
>your hands)
>-         Take a minimum rest 5', 6' or 7' between your deep dives
>-         Don't realize the max depth at the end of the training
>-         Try to go down and up with the maximum relaxed movments you can
>do (no effort)
>-         No deep dive when you are tired
>-         If you feel a little bad after a deep dive, take Oxygene and
>tell your friends to observe you, if bad sensations persist, go to the
hospital
>-         Use a depth gauge to ckeck and register the frequency of dives
>(depth, dive time and number in one our)
>-         Planify your training to avoid stupid improvised trainings
>
>Claude Chapuis


DPTNST,


John