Looking for research/opinions on specific bounce dives

[Kharon]

Later this year my club is doing it's annual "Clean the Lake" dive. One of the members stated that it's very dangerous to bounce dive. My opinion was that it's not dangerous at all if you are picking waste at 10-20 feet and once in a while carrying your bag up to a boat to be emptied - as long as you do a slow ascent. My thinking is that at those depths you aren't accumulating much N over the course of an hour or so and will be far from NDL throughout the dive.

Now - I would like to know if I am wrong. During milfoil remediation we commonly dove those depths over the course of 2 days in the water about 8 hours each day with frequent trips to the surface. No one ever had a problem. But I don't want to make a statement that is incorrect and cause someone a problem.

I am especially looking for links to research that gives a relatively clear picture/answer. Opinions are, of course, welcome, but research is what will be convincing.

 

[KeithG]

I thought you would be okay, but maybe not?

[abstract] DECOMPRESSION SICKNESS AFTER TWO EXCEPTIONAL EXPOSURE DIVES IN SHALLOW WATER

 

[TMHeimer]

Hmmm. I do a lot of very shallow diving and frequently ascend to check my location. But most of the time from 10' and occasionally from 15, once in a while from 20-30. No problems yet, assuming it is just too shallow. But I at times do ascend a couple of times with less than 10 mins. in between. For me and my shell collecting, it is easier than constantly using the compass, since I purposely get turned around quite a bit. Something to think about though. For sure I could ascend fewer times.

 

[scubadada]

I thought you would be okay, but maybe not?

[abstract] DECOMPRESSION SICKNESS AFTER TWO EXCEPTIONAL EXPOSURE DIVES IN SHALLOW WATER

It looks like the first day could have easily resulted in deco obligations

 

[stuartv]

According to Subsurface, you could stay down at 20' for 8 hours straight, on air, and still ascend directly to the surface without exceeding 80% of the M-value of any compartment (Buhlmann ZHL-16C model).

Personally, I would not worry about going up and down to 20' or less all day.

There is, I think, evidence to support that multiple bounce dives to "significant" depths is not a good idea. Basically, the models aren't well researched for that kind of thing. But, when the depth is so shallow that you could never accumulate enough nitrogen to result in getting bent (according to the Buhlmann model, anyway), I wouldn't think it it is an issue.

 

[KevinNM]

You can, in theory at least, get DCS from doing short deepish bounce dives soon after a deep dive. You crush existing bubbles such that they can make it into the arteries. If it's all shallow stuff that doesn't seem very possible.

 

[The Chairman]

There's bounce diving and then there's bounce diving.

The abstract calls 45 minutes at depth a bounce dive. I would disagree. A bounce dive is a straight ascent right after you've reached the bottom. Dive a PDC, ascend slowly and carry a mesh bag for the trash to reduce trips to the boat and you should be fine. I think you would have more issues with hypothermia than DCS.

 

[Steve_C]

There is no indication of how fast the individual went back to the surface. During each of the 20 dives there was likely a fair amount of physical exertion. After the dives there were no symptoms but then the individual went and was physically active for a couple hours. Sounds like they were pushing it.

 

[stuartv]

I call a bounce dive anything that's not a saturation dive.

 

[Steve_C]

I call a bounce dive anything that's not a saturation dive.

If all recreational dives are bounce dives then the term has very little meaning.