"Bouncing"

[gcbryan]

Speaking purely about theory, I seem to recall from previous posts that fast tissues like blood only take 2-3 minutes to saturate, and since the process is exponential, even one minute at depth gets you most of the way there. Also as Thal pointed out, Doppler studies have showed bubbling on just about any dive. IIRC, other Doppler studies have also found that the maximum number of detectable bubbles seems to be about 50 (to 60?) minutes after surfacing. However, I don't know how true this might be if someone hasn't been under pressure long enough for tissues other than blood to pick up significant amounts of oxygen. Nevertheless, if the former is true, all this might suggest that even with a short dive, an SI of 60+ minutes might be a good precaution. OTOH, if other tissues really aren't offgassing into the blood stream, maybe only 5-6 half times for the blood alone (15-20 minutes?) might be needed. Either way, I'm wondering if after a bounce, even if it's the first dive of the day, a decent SI afterwords might not be a bad idea.

If the half-time of blood is 2-3 minutes as far as ongassing that's also the half-time for offgassing so that isn't really an issue.

 

[lamont]

you can't just deco out the bounce dive, you have to deco out the bounce, plus the previous dives and all the free phase bubble shower you got surfacing from the last dive.

if you don't understand that, you're gonna get bent bounce diving, and shouldn't do it.

 

[AndrewA]

While a bounce dive at the beginning of the day is not in itself dangerous you have to remember that it is a dive and needs to be factored into the planning of all subsequent dives. The effect on NDL on what would otherwise be your first dive of the day is significant.

 

[ZenDiver.3D]

On my boat, we have one wreck at 50 meters, that we have find. We have a dm or instructor who rides, not to dive, but to set the line or check the anchor. We have one go just to locate and run the line from the conn tower to the bouy we put out. That guy/gal does that and returns. They then go back after the two dives, to remove the line and make sure the anchor is free to pull. Not a problem, as they don't do any other dive.

After night dives, our mate only has to drop 6 meters to grab the strobe.

Knowing what is acceptable to do here, should come with the dm or mate territory. It isn't exactly a model for diving, so don't always do as they do........ Ask why, and follow your training.

 

[Thalassamania]

While a bounce dive at the beginning of the day is not in itself dangerous you have to remember that it is a dive and needs to be factored into the planning of all subsequent dives. The effect on NDL on what would otherwise be your first dive of the day is significant.

It must be kept in mind, however, that TWO bounce dives, back to back can present a real problem.

 

[seaducer]

Speaking purely about theory, I seem to recall from previous posts that fast tissues like blood only take 2-3 minutes to saturate, and since the process is exponential, even one minute at depth gets you most of the way there. Also as Thal pointed out, Doppler studies have showed bubbling on just about any dive. IIRC, other Doppler studies have also found that the maximum number of detectable bubbles seems to be about 50 (to 60?) minutes after surfacing. However, I don't know how true this might be if someone hasn't been under pressure long enough for tissues other than blood to pick up significant amounts of oxygen. Nevertheless, if the former is true, all this might suggest that even with a short dive, an SI of 60+ minutes might be a good precaution. OTOH, if other tissues really aren't offgassing into the blood stream, maybe only 5-6 half times for the blood alone (15-20 minutes?) might be needed. Either way, I'm wondering if after a bounce, even if it's the first dive of the day, a decent SI afterwords might not be a bad idea.

Actually Doppler studies have shown bubbles on the low pressure side of joints in people who never dive. I suppose the point is that silent bubbles are everywhere.

IIRC bubbles increase in the first 15-30 minutes after a dive then level out and offgas. In Deco for Divers they site studies showing that a no stop diver has bubbles for up to 2 hours after, a safety stop diver less bubbles for less time, and a diver who did more stops and a slower ascent even less bubbles that lasted less than an hour.

Maybe this is why bounce dives to clear the wreck are always done by the DM with the least seniority?