Fast ascend

[DandyDon]

And if Pooldive is in Australia, we'll have to get someone from Oz to explaine.

 

[fire_diver]

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?
I had no simptons and my instructor said it was no problem, just in case I decided not to di my second dive.
Thanks for your oppinions.

In my opinion, I think you will be fine. Just be sure to use this as a learning experience. With the suit you were wearing, and the tank usined, you need more lead. You should never have trouble going under at the start of a dive.

Now to your question. DCS is cuased by bubble formation where they shouldn't be, right? Think about opening a bottle of soda or bottle of champaign. If you "pop" the cork, the bubbles form so fast that the contents spray out. If you hold on, slowly let the pressure out, then everything is fine. The contents just bubble slowly and safely.
A good thing to think about when you start diving deeper.

-Comrade Stroke

 

[Crazy Fingers]

Well the UK and the US are seperated by a common language. :lol2: Some of the wordings y'all use throw me at times. I often have to stop my Scottish friend for explanations.

I read "...that DCS is all to do with ascent rate and not whether you stayed inside NDLs or not" as suggesting that exceeding an NDL would not lead to DCS - but it could. Either exceeding NDL or Rapid Ascent or worse both can.

I think String said exactly what you think he said, and I think he was right.

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.

Put another way, it's a combination of ascent rate, depth, and time that gives the NDL. Since ascent rate is forced to be 30 fpm as an arbitrary standard, we ignore the other possibilities and just consider depth and time. This is just the standard we've grown accustomed to. Not that there's anything wrong with that, as I like 30 fpm just fine. But that still doesn't mean it's anything more than half of 60 fpm, which was the speed of U.S. Navy cranes cranking people out of the water.

Hmm... did I just discover the next big breakthrough in dive computers??? Choose your own adventure: 5 fpm ascent rate or a deco stop at 10' for 10 minutes!!

 

[String]

Not strictly true. Each table works slightly differently and is defined slightly differently but generally have a maximum AND a minimum ascent rate to stay within the model - in other words the NDLs are calculated within a band of rates, stray from it either way and the model is no longer meaningful. For example a slower ascent rate from depth could mean MORE on gassing as it takes longer to reach the depth where off gassing starts and so on.

You cant increase an NDL of a table by just coming up slower from it. At least not a direct relationship.

 

[DandyDon]

Conversely, it very well could be that your NDL is 75 minutes at 60 feet if your ascent rate is a measly 10 fpm.

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.

 

[Skull]

I just read in the accident threads where a giver executed a shallow test dive ...stayed within the NDL's and preformed a safety stop and STILL suffered DCS ...analysis ...DEHYDRATION... which I am sure is the main contributing element in most DCS cases.

 

[PoolDiver]

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.

Now, coming back to theory, as the Open Water diver does not give much info on this subject I have to make reference to the User Manual of the Suunto Mosquito.
If you exceed NDL then the computer calculates the necesary stops with ceilings and floors. This was not my case. If you temporarily exceed the ascent rate, then the computer will extend the time of the safety stop, converting iy into a Mandatory safety stop. If you still do not comply with this stop, then the computer would penalize you in the calculations if you are plannig a consecutive dive. If, however, you fail to comply with the mandatory stops once you have exceeded the NDL, then, the computer goes into Error mode and locks for diving during 48hs.

Thanks everybody for your answers.

Now,

 

[spectrum]

PoolDiver,

We're glad to hear that no symptoms materialized and that you're doing fine.

If you went from a 1 to a 2 PC suit of the same or thicker material that would leave you under weighted, there is no maybe about it. Having difficulty starting your dive with the weight of a full cylinder should be a red flag. Be sure to do a proper weight check and to allow add the 5 pounds or so for consumed air before diving again.

As far as the computer goes you went several levels into contingency routines and it reached the point where it could not assure a safe outcome for a future dive hence the lock-out.

Pete

 

[PoolDiver]

Maybe I was not clear. The computer did not lock out. As a matter of fact ,despite any penalities added it allowed to continue diving if I wanted to ! Just in case I decided not to. I've learned the lesson for next time.

 

[String]

As the suunto literature itself states though, if you exceed ascent rates it'll add on stops and so on BUT also says you're outside the limits of the algorythm. So just because the computer doesnt error doesnt mean its happy about it, merely it was in best-guess mode after being pushed beyond the limits of the mathmatical model it uses.