A questions about "bouncing"

[Liquid]

Blacknet-

by definition: A RECREATIONAL NDL diving table is a table that alows a DIRECT ascent to the surface at any given point of the dive. I'll take it even a further step, and tell you that the asumption behind the tables, is that if something happens you are also safe to do an emergency ascent. In that case, no further diving should be done for at least a day.

This is by no means an encouragement to neglect any correct ascending/safety stop procedure!!!

Those measures are taken to give the diver a better safety margine. I alwais take them, unless something forbids me to (I wont make a safety stop in the middle of a swarm of jelly-fish, for example). Ascending slowly Is very important, and I wouldn't dive without ascending slowly. But safety stop is a RECOMENDATION. It's not obligatory. And still, I almost alwais do a stop (well, ususaly my dives end at the shore, so I simply dive a bit in the shallow area).

 

[rcohn]

Since someone might actually believe NetDoc's claim that Rodale's declared "bounce" and "sea-saw" profiles to be ok,

I think it was in Rodale's this past year (but I really can't remember) that they debunked a bunch of myths. The "bounce", the "sea-saw" and the "reverse profile" dives were all cleared as being safe. That is... IF you use a computer to track everything. I have had to do several bounces when I am working with students, and instructors do this regularly when practicing controlled emergency ascents with students. Just make sure you really go with the NEW ascent rate of 30 fpm instead of 60 fpm!!!

I decided to do a little research and found these three Rodale's articles on reverse profiles. Only reverse profiles are discussed and Rodale's (and later the "Reverse Dive Profiles Workshop") conclude that they do not significantly increase the risk of DCS. Note that the workshop did place some limits on reverse profiles for safety.
http://www.scubadiving.com/training/instruction/deepdive2.shtml
http://www.scubadiving.com/training/instruction/profiles.shtml
http://www.scubadiving.com/gear/computerQA.shtml

The only mention of the bounce and sawtooth profiles.

Divers are going to use dive computers and they are going to do reverse profiles, sawtooth dives and bounce dives, so let's explore what the opportunities, limits and risks are and quit hiding our heads in the sand.

, was in defense of the questioning of standard safety recommendations, not a declaration that they are all safe. Using a search on the term bounce, I could find no specific recommendations by Rodale's on their safety. They do note in their computer reviews that bounce and sawtooth profiles are included in their testing protocol.

I know this is the Internet (the greatest source of misinformation ever conceived) and it's fun typing the first thing that floats into your head, but it might be nice if people checked their sources before advising divers that potentially dangerous practices have been declared safe by a "reputable" authority. Someone might actually take you seriously.

Ralph

 

[Dr Deco]

Dear Lost Yooper:

This is commonly believed, but one of the things taught to us by Doppler bubble research studies is that the lung filter retards gas bubbles even when they are compressed. It must be remembered that bubbles in capillaries are cylinders and not spherical. Compression shortens these bubbles but does not decrease their diameter in the lung capillaries. The filter still works - - thank heavens for this.

The recompression of descent is not what contributes (most of the time) to neurological problems for recreational divers.

Dr Deco

 

[Liquid]

Dr Deco,

I find your last reply very interesting. Can you point me to some more about this behavior of bubbles? (the spherical issue)

I wasn't aware of that, but it makes perfect sense!

A question doc-
Those spherical bubbles, that do get absorbed by the lungs, what are they considered?
I find it hard to belive these are micro bubbles, since they are filling the capaleria. How often does it happen to have such bubbles?

I got a ton more questions, so better point me to a good site

 

[Dr Deco]

Dear Liquid:

The behavior of bubbles of which I was speaking is most easily found in the THIRD edition (1982) of Bennett and Elliott “The Physiology and Medicine of Diving.” It is in Chapter 16 entitled “Ultrasonic Surveillance of Decompression” by Powell, Spencer, and von Ramm. It has photos of the bubbles in capillaries, and you might find it at a university library.

The bubbles are eventually “absorbed” by the lungs as the free gas passes from the cylindrical bubble in the capillary into the alveolus of the lung. It shrinks down because the surface tension in the bubble causes the gas inside to be at a higher pressure than the gas outside.

These bubbles are trapped in the lung capillaries every time a gas phase is formed in fat and muscle capillaries and moves through the venous return (vena cava) to the lungs. These are the Doppler bubbles referred to so often in the diving literature.

I hope you are able to find the book chapter.

Dr Deco

 

[Liquid]

Thx doc.
I'm going to check my university library to see if they got the book.