Any danger from several shallow dives in a row?
- Thread starter Jarrett
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*Floater*
Contributor
Jarrett:
He said the student had trouble staying below the surface, so I assume she kept popping back up once she added air to her BC and the DM would follow and bring her back down. He said they were only going down to about 10-15 FSW depth on descents, and he only went up and down 3-4 times. A little bit after the dive his arm went numb and limp, and the DCS symptoms kicked in hard. He got treatment, but still couldn't dive a month after the incident when I was there. The docs told him that he may never be able to dive again. As far as I know the student was fine.
Note: This is just based on what he told me - I wasn't there when it happened - I don't know other circumstances that might have come into play.
Charlie99
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Jarrett, unfortunately, DCS is a probabalistic, i.e. chance, luck, semi-random, only partially predictable.Jarrett:
Multiple ups and downs increase your risk, particularly if any of the earlier ascents has been too fast.
Your Aeris Atmos computer is a simple neo-Haldanian model that doesn't take microbubbles into account --- even a 1,000 foot per minute ascent won't bother it in the least. You have to personally add in extra fudge factors to account for "misbehaviors" like multiple descents and ascents, or sawtooth profiles. Just because your computer only showed 2 bars does NOT mean that everything is fine.
One one hand, the sort of profile you describe isn't that much different that what a lot of instructors do when teaching classes. On the other hand, a lot of instructors will tell you that this sort of up and down stuff leaves them beat and tired at the end of the day.
Your profiles fall into that huge grey zone between safe and unsafe. I'd do them if there was a compelling reason to do so, but I'd avoid them if possible.
You should find another way to get your daughter comfortable in the water.
**NOTE**
This is a resort DM. These people are in the water almost every single day. During the high season it probably is every single day. There is a whole lot more to this story than anyone but those involved know.
TwoBit
This is a resort DM. These people are in the water almost every single day. During the high season it probably is every single day. There is a whole lot more to this story than anyone but those involved know.
TwoBit
lamont
Contributor
when you look at profiles for rescue classes, ascent drills, or instructors doing CESAs for students its kind of comparable to what you're doing.
usually when the plan is bounce diving like that the depths need to be kept pretty shallow, times need to be kept shorter, you should still try to stop at 10 or 15 fsw for at least a minute, ascent rates need to be slow, and if you mess up too many times on your ascents, you should really call it a day. i think that nitrox can also help add a safety buffer (even if your daughter isn't trained for nitrox, the scuba police aren't going to pull you over for giving her a tank of EAN32 when you're diving a <= 30 fsw hard bottom).
might be better though to work on snorkelling or something to get her to the point where she's comfortable enough in the water to stay down for the duration of the tank...
usually when the plan is bounce diving like that the depths need to be kept pretty shallow, times need to be kept shorter, you should still try to stop at 10 or 15 fsw for at least a minute, ascent rates need to be slow, and if you mess up too many times on your ascents, you should really call it a day. i think that nitrox can also help add a safety buffer (even if your daughter isn't trained for nitrox, the scuba police aren't going to pull you over for giving her a tank of EAN32 when you're diving a <= 30 fsw hard bottom).
might be better though to work on snorkelling or something to get her to the point where she's comfortable enough in the water to stay down for the duration of the tank...
Damselfish
Contributor
Since this type of profile is generally considered bad, don't do it. You're kind of teaching your daughter a bad habit. Perhaps a few times shallow with slow ascents is ok, as mentioned it happens in training classes often and these actually sound like training dives in a way. If you're going to do it anyway maybe preset a limit on how many times you will do this no matter how short it winds up being or how much air you have. I don't know what the right number is but after that, out of the water for a real interval. Maybe knowing there is a limit would encourage her to stay down. (Though I'm not sure if that is a good thing either, if she would stay down longer even when uncomfortable just to be able to dive that's not good either. It sounds like to me like she isn't ready to be diving yet, at least in these conditions.)
Remember, the largest pressure change occurs in that first ATA. Although a sawtooth profile isn't recommended at all, it's safer at deeper depths because there's not as much pressure change occurring. Within the first 30' there's a lot more change occurring.
When you surface, even if just from a 3 minute dive. Get out, take your gear off and work the table. Go back in when you're back in PG A or B. It's safer diving. It will teach your daughter more responsibility (Don't make it a punishment - emphasize the safety factor). And eventually she'll get tired of all the SIs and want to stay down longer.
When you surface, even if just from a 3 minute dive. Get out, take your gear off and work the table. Go back in when you're back in PG A or B. It's safer diving. It will teach your daughter more responsibility (Don't make it a punishment - emphasize the safety factor). And eventually she'll get tired of all the SIs and want to stay down longer.
haneym
Guest
Heffey:
the reason this is different (and more dangerous) is because the biggest change in pressure is in the first atmosphere. at depth, you can descend and ascend a little faster because there is less change. many computers take this into account and will actually let you ascend a little faster at depth but will make you slow as you surface. going from 30' to the surface is worse than going from 130' to 100'. at least thats what i learned.
Sideband
Guest
If a student in one of our classes showed that much discomfort we would tell them they should come back to the pool another time or two. We would hopefully catch that while still in confined water but if they made it to OW and had to keep surfacing because of nerves we would not certify them that weekend. That's a potential accident waiting to happen. She sure doesn't sound capable of handeling a problem underwater should something happen to you. You might consider furthering your training through Rescue while keeping her in the pool until her comfort level comes up to the point that she can complete a single dive. May not be what you want to hear but I think it's a safe track.
Joe
Joe
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