When, if ever is it safe for a diver to make multiple trips from the bottom to surface in one dive?

[DiveProKoko]

Here is one of my profiles from doing air sharing ascents with students. Haha! They did pretty good! Only one rapid ascent warning

 

[Nitrox_DiverNY]

Serviced 5 fore and aft moorings for 4 hours on a dive last week. Up and down cleaning rope clearing chain, replacing swivels and shackles. It is an absolute killer on your sinuses. Don't do it if you have any kind of sinus problem otherwise your good to go.

thanks for the reply. Sounds interesting servicing moorings and replacing shackles underwater. We use moorings here in NY, when I had the boat me and the mooring guy would take them out every season and its a pain to take them out every year, sounds like in a way servicing in the water would maybe be better.

 

[tursiops]

Here is one of my profiles from doing air sharing ascents with students. Haha! They did pretty good! Only one rapid ascent warning


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What does it look like for CESAs?

 

[DiveProKoko]

What does it look like for CESAs?

Same...with more rapid ascent warnings.....because while you're trying to not ascend TOO rapidly, it's inevitable. LOL

 

[Doby45]

Here is one of my profiles from doing air sharing ascents with students. Haha! They did pretty good! Only one rapid ascent warning


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Man I was going to say the same thing. I have done so many class air-shares and CESAs that if I kept the log it would look like a heartbeat.

 

[Esprise Me]

My understanding (someone please correct me if I'm wrong; I don't consider myself an expert by any means!) is that, while there's a lot of anecdotal evidence supporting the safety of repeated ascents, there's also a fair amount of anecdotal evidence to the contrary, and not nearly as much actual research as there is behind more typical dive profiles. So yeah, popping up once or twice (slowly!) during a shallow dive to get your bearings is very unlikely to cause a problem. But as the number of ascents increases, so does the uncertainty.

Coincidentally (given your username), it occurs to me that diving a sawtooth profile might be a rare case where using Nitrox improves safety even at shallow depths. If you're diving 32%, the equivalent air depth on a 30-foot dive is only 21 feet; on a 10-foot dive, it's only 4 feet. And of course, you can go with a richer mix if it's available without bumping up against the MOD. If you go with 40%, your EAD for a 30-foot dive is 15 feet, and at 10 feet you're effectively at the surface. Might make a difference if you're bouncing up and down for hours.

 

[lowflyer]

I can personally attest to the fact that shooting up and down in the water column from about 30-35 feet can be dangerous, having once suffered inner ear barotrauma with complete loss of hearing in my right ear. The hearing mostly gradually returned after about 6 months. I have a friend who is an instructor and who suffered the same injury.

It's possible my right ear was not clearing well. I was thoroughly worked up and described this event here several years ago so will let it go, but I would suggest not being cavalier about what is possible to happen.

 

[Nitrox_DiverNY]

My understanding (someone please correct me if I'm wrong; I don't consider myself an expert by any means!) is that, while there's a lot of anecdotal evidence supporting the safety of repeated ascents, there's also a fair amount of anecdotal evidence to the contrary, and not nearly as much actual research as there is behind more typical dive profiles. So yeah, popping up once or twice (slowly!) during a shallow dive to get your bearings is very unlikely to cause a problem. But as the number of ascents increases, so does the uncertainty.

Coincidentally (given your username), it occurs to me that diving a sawtooth profile might be a rare case where using Nitrox improves safety even at shallow depths. If you're diving 32%, the equivalent air depth on a 30-foot dive is only 21 feet; on a 10-foot dive, it's only 4 feet. And of course, you can go with a richer mix if it's available without bumping up against the MOD. If you go with 40%, your EAD for a 30-foot dive is 15 feet, and at 10 feet you're effectively at the surface. Might make a difference if you're bouncing up and down for hours.

thanks for your feedback, it would be interesting to see more research on these kinds of profiles and how they correlate to DCS, and I agree about the Nitrox, it adds a little safety buffer. I always try to dive 38% plus for that protection it might offer even with a normal profile

 

[Nitrox_DiverNY]

I can personally attest to the fact that shooting up and down in the water column from about 30-35 feet can be dangerous, having once suffered inner ear barotrauma with complete loss of hearing in my right ear. The hearing mostly gradually returned after about 6 months. I have a friend who is an instructor and who suffered the same injury.

It's possible my right ear was not clearing well. I was thoroughly worked up and described this event here several years ago so will let it go, but I would suggest not being cavalier about what is possible to happen.

im glad your hearing came back! that must have been a very scary experience! its definitely not good to be to cavalier in diving and good to know the risk. Thanks for sharing

 

[JXT71]

Hello all, newbie diver question here.. After witnessing divers make multiple trips from the bottom to surface in about 30ft of sea water, I have been asking myself how much risk this creates in a dive profile and how common is this profile. I assume it creates more DSC risk but wanted to see if anyone here could elaborate on it more. There must be certain divers that dive this way for recovery or for special working conditions.

At what point after ascending from depth (not counting NDL or gas left) is it unacceptable to return back to depth on the same dive? How many times can this be done in one dive?

Lets say If a situation arose where a diver was at 30ft, then had ascended to surface for some visual aid to lets say shore, then decided to descend back down to 30ft for the remainder of the dive, is this a safe action taken by the diver?



Thanks for the feedback!

Sure, I've had to do some bounce diving on my dive job. In particular, it involved me cleaning a 30-40ft pool over two or so tanks (about 2 hours) while other people did construction work on a structure overhanging the pool (without going into detail, it was safer than it sounds). In the event they dropped a nut or bolt, I would bring it to the surface and continue my work below.

Going off tables, I don't think anything would outright say it's unacceptable to return to depth on the same dive (within your basic rec profile), but when I had a sawtooth dive pattern I certainly FELT it was becoming unacceptable. I'd say it increases the risk of a DCI in general. I would experience nausea and feel pressure build in my sinuses more rapidly. It would quickly become an uncomfortable dive if I had to surface more than three or so times, and left me with the impression that I shouldn't be diving that way too often.

I've also had a dive similar to what you described on the last point: I was returning to shore after diving around 70-80ft, and I had to cross a canyon that would leave me no reference underwater. So I surfaced to get a compass heading before returning to 30ft. No ill effects. Not the ideal method, but hey - what's the point of being overly conservative if not for having a buffer for such occasions?