up too fast? go back and do it again ???

[jagfish]

The rumor mill suggests that several WKPP support divers were bent doing equipment retrieval bounce dives (source: GI's web page).

Heard the same rumor...

 

[Thalassamania]

Current U.S.N. protocol is (If memory serves):

If the diver realizes that they have broken the no-D limit, but have not surfaced, and do not have tables with them stop at 10-15 ft for 15 mins or until 300 PSI. Breathe a minimum of 30 min pure O2 and 12 hours of observation with no diving. Any symptoms mean a chamber ride.

If the diver does not realize that they have broken the no-D limit, and has surfaced of is not carrying enough gas to perform decompression and is symptomatic, within 5 mins may return to water with a new gas supply, to the depth of the missed stop for 1.5 times the required stop. If the diver cannot return to the water, breathe 60min of oxygen. If no symptoms occur, 12 hours of observation with no diving. Any symptoms mean a chamber ride.

If the diver is symptomatic and can’t return to the water and a chamber is within 1 hour, time for a ride (table five or six).

 

[Charlie99]

Because in water re-decompression can be dangerous.

The difference between in-water recompression and going back down and doing omitted decompression is whether or not you have symptoms of DCS.

Going back down; in a controlled manner, with plenty of gas, to do omitted decompression (or any other stops or slow ascents you desire) is a good idea. Going back down to recompress to treat DCS is a bad idea unless you have no other choice.

The official CMAS procedure is that once you have regained control of your ascent you stay at current depth for the length of time it would have taken you to get there with a normal ascent (10 m/min). Then you proceed to your safety stop (assuming that you are within NDL).
However, if you reach the surface after an uncontrolled ascent (a more common problem), the procedure is to go back down to half of you maximum depth, spend five minutes at that depth, and then proceed to the surface and do your deco stops (if any) as if you had spent the entire time necessary for the procedure at your maximum

This looks like a couple of pretty simple yet effective procedures. Too bad these sort of procedure aren't as clearly taught by other agencies.

 

[Vayu]

whether or not you have symptoms of DCS.

I see what you are saying but it is a pretty thin line between the two. Considering most divers with DCI are in some form of denial, or do not recognize the signs of their conditions - such as sub-clinical DCS or a few of the more subtle neurological clues - within themselves, I would not be too quick to try this or to let any of my purely recreational buddies try to do it without a doctor or a chamber nearby. It is likely that damage is already done and a bottle of 02 will be safer.

-V

 

[Thalassamania]

There is no doubt about the problems with a bounce dive after a dive. This is especially true of clearing the anchor after surfacing. Over the years there have been MANY observed cases of "undeserved" DCS that were thought to result from this.

 

[*Floater*]

Very interesting topic. I'll make sure to ask an instructor about this, but my current instinct would have been to re-descend to the missed stop depth or further down (gas supply and other factors permitting of course) in order to compress the bubbles that had formed and potentially gotten lodged in tissues, and then ascend very slowly and carefully in order to give my body time to off-gas them properly.

I had thought the problem with the bounce diving was the quick second ascent - you bubble at the surface and those bubbles are growing, then you go down again so they compress and slip into your brain, spine, etc. but then you bounce up so fast that they don't have time to come out and instead expand in those tissues wrecking havoc. If you just went back down far enough to compress them, and then came up slowly enough to give your body time to off-gas them, then you should be fine.

But this is only based on my very limited understanding of the subject. I'll make sure to discuss it further with knowledgeable people.

 

[espenskogen]

Very interesting topic. I'll make sure to ask an instructor about this, but my current instinct would have been to re-descend to the missed stop depth or further down (gas supply and other factors permitting of course) in order to compress the bubbles that had formed and potentially gotten lodged in tissues, and then ascend very slowly and carefully in order to give my body time to off-gas them properly.

I had thought the problem with the bounce diving was the quick second ascent - you bubble at the surface and those bubbles are growing, then you go down again so they compress and slip into your brain, spine, etc. but then you bounce up so fast that they don't have time to come out and instead expand in those tissues wrecking havoc. If you just went back down far enough to compress them, and then came up slowly enough to give your body time to off-gas them, then you should be fine.

But this is only based on my very limited understanding of the subject. I'll make sure to discuss it further with knowledgeable people.

The TDI Procedure is to ascend to the depth of the deepest missed stop, and start your schedule again x 1.5 times - So for each 2 minute stop, you do 3, etc...

Now as mentioned above, this only applies to missed stops (i.e no symptoms).

In the case of DCS symptoms, I believe the procedure is give O2, and activate EMS.

E

 

[Mike Newman]

I heard an answer to this in some recent training...

If bubbles had been formed on your rapid ascent, they would be confined to the "pulmonary" side of your heart and will hopefully be released through the alveoli in the lungs, allowing the diver to remain asymptomatic.

If one descends again, the bubbles will reduce in size, and may be able to pass by the lungs and into the side of the heart that pumps to the brain. At this time, the diver would have micro bubbles in the total circulation system, including neural tissue.

If the diver now ascends before these micro bubbles are completely purged from the blood, one or more of them could expand in neural tissue upon final final ascent.

For this reason, I was advised to never re-descend in this kind of situation.

This is also apparently the mechanism of danger in bounce dives.

Jagfish - thanks for this info - the logic behind the drill is always valuable to have.