Fast ascend

[DandyDon]

Thanks everybody for your answers. It turned out to be a very interesting matter. I'm feeling just fine. DanyDon, I'm in CHile and water temperature at 20mts was 13C. I've been diving for only a few months and this was my first and last experience of this sort. I usually use 12kgs of lead but today I was wearing a 2 piece suit, maybe that was it.

Happy to hear that you feel ok. Time is crucial when treatment is needed, and I am very glad you didn't.

Hope you enjoy SB now, learn lots, and all. How about putting your location and dive experinece into your profile for future discusssions, and go to Introductions forum to post one if you'd like?

 

[randini]

Glad to hear you're OK. Very few chambers in Chile

When you lost control of your buoyancy, did you have any air in your BC? Seems strange that is was so sudden like that and after only 1/2 hour in only 30ft (you still should have had plenty of air left). I ask becasue I have a reg with a high pressure creep. Last time I used it, it was filling my BC constantly until I just unplugged it. Now that reg won't get used again until I get around to getting it fixed. My point is check out the gear you were using to make sure there wasn't some malfunction that you didn't notice.

Oh and saludos de Chile.

 

[String]

IP creep should at worst cause a reg to freeflow not trigger an inflation.

BCs slowly filling usually more due to sand/grit stuck in the actual inflator mechanism holding it slightly open.

 

[randini]

Good point, but bn my case it was doing both. The inflator might be a bit sticky and have contributed to my BC filling as well, but the creep was there. I did have a constant flow coming out of the reg as well, not quite a full on free flow, but there was constant air coming out of the 2nd stage. Either way that reg is going to the shop next time I head to the city and have the $ for an overhaul.

My point was that OP should also have a good look at the gear he/she was using and make sure it's just a matter of being underweighted.

 

[Blackwood]

Question: Does decompresion sicknes occur due to a rapid ascent or is it mainly caused by exceeding non decompression times and not respecting the mandatory safety stops?

No one knows for sure, but I'm in the camp that believes it has much more to do with how you ascend (stops included, "mandatory" or not) than anything.

 

[String]

I've witnessed ip creep a lot and generally it either causes a freeflow or if someone is breathing from a reg on the 1st stage at the time, nothing happens.
I've heard of exactly one incident with creep causing an inflator sticking and that was due to 2 extremely badly tuned second stages that werent being used and tuned down as a result.

99% sure it'll be your inflator causing issues to fill the BC.


I'd also say with modern gear its EXTREMELY unlikely to be equipment causing it. Underweight or overweight far more likely (overweight generally causes faster uncontrolled ascents. Underweight just means someone cant stop. Usually anyway).

 

[Charlie99]

Look at it like this: the table you have gives you very, very low risk of DCS if you follow what it says, and that is 30 fpm ascent rate and say 50 minutes at 60 feet. If you blow the ascent rate, the 50 minutes isn't valid any longer. If your ascent rate was 60 fpm, your NDL might be 20 minutes at 60 feet. Conversely, it very well could be that your NDL is 75 minutes at 60 feet if your ascent rate is a measly 10 fpm.

Although not directly on topic, the above statement is far enough from the truth that it deserves correction. It is INCORRECT. 75 minutes at 60' then ascend at 10fpm is well beyond limits.

SLOWER IS NOT ALWAYS BETTER.

If you ascend significantly slower than the rate the tables are designed for, the dive becomes a multilevel dive and needs to be calculated as such.

The other statement: "If your ascent rate was 60 fpm, your NDL might be 20 minutes at 60 feet." is also incorrect. Both USN tables and for many years, the DSAT/PADI RDP have had limits of 60 and 55 minutes at 60', with 60fpm ascent.

In other words, the 60' NDL does not radically change from 20 minutes to 50 minutes to 75 minutes as ascent rate goes from 60fpm to 30fpm to 10fpm.

 

[Crazy Fingers]

Excuse me, but that is just wrong. Some goats were killed proving that didn't work well. On any chart, 75 min at 60 is beyond No Decompression Limits and decompression procedures with stops are indicated.

It's 20 minutes beyond NDL on the Padi OW chart. USN Dive Table #5 indicates 7 minute stop at 10 feet, my TDI book uses the same tables, and I cannot use my computer for a sea level deco plan at the moment as I am at 3,300 ft and it adjust automatically.

More recent studies encourage an additional 1 min stop at 30 ft, but slow ascents alone are not suggested for such significant deco obligations.

But this is really distracting from the OP's question. He had 28 minutes at slightly deeper than 30 ft, for which Padi gives a 205 minutes NDL - so for his case it is all about ascent rate, his being uncontrolled and excessive.

Of course none of the tables show 75 minutes @ 60 feet! That was my point... all the rec tables are made for a maximum ascent rate of 30 fpm. If there was a table which said your maximum ascent rate was 10 fpm, it could have a longer NDL. This is because you're outgassing for a longer period of time as you are surfacing. The 75 minute was just a number I pulled out of my arse. Of course I don't know what the "real" NDL would be because I don't have any research on it. This is why I also would not try doing this, it's just a theoretical argument.

However, as String pointed out, the idea gets monkeyed up a little because there are depths at which below you will not outgas at any rate. But it would just require adjustment to the NDLs at deeper depths.

I'm just saying... if we made the Crazy Dandy Don Fingers table, specified an ascent rate of 10 fpm, and tortured animals to get the data, I bet you five bucks that the NDLs would be longer than what is printed with a 30 fpm table. If we specified 100 fpm, they'd be a lot shorter.

 

[String]

One of the oddest things to get used to on my deco procedures course was conciously ascending a lot faster than i'd normally do for the deeper stops segment.
So used to "slow is better mantra" when you end up doing dives where timing and rates are crucial its very hard to change mindset.
The first few dives it felt very odd, deliberately going fast despite a very long deco obligation.

 

[Crazy Fingers]

One of the oddest things to get used to on my deco procedures course was conciously ascending a lot faster than i'd normally do for the deeper stops segment.
So used to "slow is better mantra" when you end up doing dives where timing and rates are crucial its very hard to change mindset.
The first few dives it felt very odd, deliberately going fast despite a very long deco obligation.

Well, I think there's something else going on there. And that's running out of air! Once you reach the point where you are offgassing, the safest course of action from a DCS perspective would be to go slow to each stop, spend the required time there, and then continue slowly to the next stop. Right? I don't see how ascending faster could possibly make you safer, except....

The problem with that is that since you are deco diving, you had to plan everything out to make sure you have enough gas. So I guess they just don't want you dilly-dallying between stops and wasting gas you didn't plan on using.