Alert diver article on Deep Stops

[MXGratefulDiver]

The fact is there are still "undeserved" DCI (PFO for example) hits and I dont think you can pad the current models enough to make it practical to totally reduce the risks.

But a hit due to PFO wouldn't be an "undeserved" hit ... there is a clearly identifiable reason why it happened.

You can never eliminate the risks ... there are simply too many variables involved, and too many potential situations to prepare for.

All you can do is play the odds, and take actions to reduce the risks to what you consider an acceptable level.

... Bob (Grateful Diver)

 

[TSandM]

That essay by Burge is one of the most frightening things I have ever read.

 

[Sloth]

But a hit due to PFO wouldn't be an "undeserved" hit ... there is a clearly identifiable reason why it happened.

That's a fair point Bob.

 

[Slamfire]

That's kind of my point. Some people dont like the term undeserved hit thinking that if they follow the rules they will be ok. Bottom line there are too many variables to ever say with 100% certain that if you only stay down so long or ascend no faster then X you wont get a DCS.

Agreed. Yet treatment for DCS is to take you down and make you ascend really slow in a decompression chamber. So it would seem logical that increasing conservatism would decrease DCS incidence.

What I understood from the article you mention is that the expected DCS decrease didn't happen.

• Back in the olden days USN tables said 60ft for 60mins NDL
• Then PADI's RDP came by saying 60ft for 55 mins
• Now most divers use computers say something even more conservative. Mine says 60ft 48mins at its least conservative setting.

From 60 mins to 48 mins there's a 20% decrease. There was no such decrease in DCS. Because there are so many more variables tied to DCS, let's look at another one. The recommended ascent rate for USN, RDP and my computer is the same 30ft/min. Maybe we should think about changing the rules on that and seeing if there is a decrease in DCS. If that doesn't work either, we should look on other factors.

Honestly though DCS is like what number three on diving accidents? Number one drowning - people panic or have a heart attack and drown. Number two AGE - people ascending to fast. DCS is so unlikely I don't really understand why people spend so much time worrying about it.

Even though some instructors do not teach about it in OW courses, I believe there should be a no-panic rule. If followed that rule would reduce drownings. Heart attacks can happen anywhere, besides there is a rule about being in reasonable physical condition. There is also a rule about ascent speed - 30ft/min. So number 1 and 2 can be largely addressed by following existing rules. The commonality of "undeserved hits" may indicate that some of the existing rules could use a revision.

 

[boulderjohn]

What I understood from the article you mention is that the expected DCS decrease didn't happen.

• Back in the olden days USN tables said 60ft for 60mins NDL
• Then PADI's RDP came by saying 60ft for 55 mins
• Now most divers use computers say something even more conservative. Mine says 60ft 48mins at its least conservative setting.

But you are only looking at first dives. The US Navy tables were very conservative for surface intervals and subsequent dives. If you used the Navy tables for a recreational dive trip, you were spending a lot of time topside between dives.

When PADI made the RDP, it intentionally made the first dives more conservative that the Navy tables in part so that they could safely make the ensuing surface intervals/dives less conservative.

The US Navy tables used the 120 minute compartment to control the dive schedule, meaning that in theory there was a complete washout in 12 hours. The PADI RDP used the 60 minute compartment, meaning a complete washout in 6 hours. (Their research indicated that the 40 minute compartment actually controlled dives within recreational limits, but they used 60 minutes to be more conservative.)

 

[Slamfire]

You're bringing up a different, but valid point. You're disputing whether tables have really gone more conservative. Maybe the writer meant that decompression tables, not NDL tables, have gotten more conservative. In that case I would say that most recreational divers stay within the NDL limits of whatever table/computer they are using. Or at least they should if they play by the rules. If they get bent playing outside the rules, then it's not "undeserved".

Also even though computers in theory seem to be more conservative, the rounding down and square profile planning that is done when using tables introduces a great deal of conservatism.

 

[Blackwood]

One problem with this current discussion is that "conservative" in this sense is not an absolute word. It's always relative to something else.

 

[stargost]

fnfalman,
From your first post about deep stop vs multi-level, here is what I (as a very new diver) would define (for myself - hopefully I'm ok):

a) multilevel:
I need to go to this depth to see this fish/coral/piece of the wreck, etc...
Then I ascent to this shallower but well defined depth to see something else
Finally I go up little more to see something again different
There are no correlation between these 3 depths. It is a dive plan based on what you want to see and how much time you want to spend at these places

b) deep stop
- I want to go below 130ft to see these big sharks, and spend as long as possible there
- Going up there is not much to see or it is not part of the dive plan, so i need to figure out the ascent process
- either my suunto DC or the fact I don't trust my ultra not conservative Dsat oceanic DC makes me feel it is better to stop briefly at a specific depth for more appropriate offgassing. That stop depth is defined by the original depth, not by something I wanted to see at this level.


I found the deep stock article very interesting in regards to 2 others articles in the same release:
"bent in Baja" and "full treatment".
In these 2 cases of DCS, both were saying they followed their computers and they should not have any problems. But there were. In Baja went down 120ft, in second case, 100ft was max of some previous dives, last being 75, and there were a lot of dives.

So it appears that in some conditions, with maybe less conservative DC (while it is not mentioned what they were using), there are DCS cases, and pretty bad ones.
Would DCS have been avoided if the 2 persons have used a more conservative DC like a suunto, which as a matter of fact would have implied a deep stop in both cases.

 

[Sloth]

In these 2 cases of DCS, both were saying they followed their computers and they should not have any problems. But there were. In Baja went down 120ft, in second case, 100ft was max of some previous dives, last being 75, and there were a lot of dives.

So it appears that in some conditions, with maybe less conservative DC (while it is not mentioned what they were using), there are DCS cases, and pretty bad ones.
Would DCS have been avoided if the 2 persons have used a more conservative DC like a suunto, which as a matter of fact would have implied a deep stop in both cases.

I hate to say it but that says to me "know your dive profile and proper ascent plan and don't trust a computer."

 

[stargost]

>>
I hate to say it but that says to me "know your dive profile and proper ascent plan and don't trust a computer."

I agree, but especially in the case of deep stop, and at deep depth, the DC may be better at maths than me ;-) and a wrong estimate/calculation of the profile there may have you continuing on gassing while you think you carry your deep stop.

When I'm richer, I'll get a suunto, and well maybe a couple of other ones to compare what they all say - lol !