15' Safety Stop vs Minimum Deco

[Zept]

Uncle Pug said many things, including...
So why did I say the minimum deco was better?

1... 2... 3... 4. Starting the process deeper in case you need to abort.

I don't follow your reasoning here. If I were going to have a problem that would cause me to abort the dive, I would rather have it at 5m (15ft) than at 10m (30ft). If I were low on air, for example, I certainly wouldn't choose to stop at 10m. I might, depending on the circumstances, still stop at 5m, since I (and my buddy) can easily do a swimming ascent from there.

In general I prefer to abort my dives at the surface!

Go on, enlighten me.

Zept

 

[Uncle Pug]

Zept once bubbled...
I don't follow your reasoning here.

The thinking is this:

Say you have a problem develop right when you get to 15' and have to abort.... if you are one of the *safety stop for 3 at 15'* divers then you have to blow off the safety stop and ascend. But if you are one of the *minimum deco* divers and have the same problem when you reach 15' you have already done your 1 minute at 30' & 20' so all you are blowing off is the 1 minute at 10'.

That was mentioned in the thread (IIRC) but it really isn't that big of a deal for our recreational NDL dives and that is why I put it last.

It is however an important idea when one is doing staged decompression diving... but that is for another day and another forum.

 

[Zept]

Uncle Pug said...
The thinking is this:

Say you have a problem develop right when you get to 15' and have to abort.... if you are one of the *safety stop for 3 at 15'* divers then you have to blow off the safety stop and ascend. But if you are one of the *minimum deco* divers and have the same problem when you reach 15' you have already done your 1 minute at 30' & 20' so all you are blowing off is the 1 minute at 10'.

The thinking is not logical . In the second scenario, the problem is developing at least two minutes later. Unless the problem is caused by reaching 5m/15ft (expanding wetsuit?), it should develop at the same time in both scenarios. If it is an OOA problem, it should develop a few seconds earlier in the second scenario since we consume more air at depth. Methinks you are rigging the problem to justify the conclusion you wish to reach!

However I accept your other arguments.

Zept

 

[AquaTec]

so PUG looking at it from a run time point of view.

you say that the problem occured just as you reached the 15 ft stop..so from a run time point of view 3 minutes prior to surfacing

well in your scenario three minutes prior to surfacing you would be just ariving at your 30 foot stop.

so in escence the problem has now occured at your 30 foot stop

and if the 15 foot stop was planned for 5 minutes and it happend at arival then within the same time frame it would have happend 2 minutes prior to your first stop. which at 30 ft/min would put you at 90 feet deep, ;ets not even consider 60 ft/min


just raddling the can here to keep it interesting. it is all simantics though isn't it

 

[Uncle Pug]

Zept once bubbled...
Methinks you are rigging the problem to justify the conclusion you wish to reach!

.. my agenda is truth.

And as I said that particular rational was previously mentioned and it does not really make a big difference in the kinds of dives we are talking about.

Strike number 4 from your consideration.

And may you never be caught in a contrary current at 15'

 

[Uncle Pug]

AquaTec once bubbled...
so PUG looking at it from a run time point of view.

From a run time POV things might look one way.
From an environmental POV things might look different.
But as I have said... this is of no consequence for this kind of diving.

 

[Spectre]

Uncle Pug once bubbled...
Say you have a problem develop right when you get to 15' and have to abort.... if you are one of the *safety stop for 3 at 15'* divers then you have to blow off the safety stop and ascend. But if you are one of the *minimum deco* divers and have the same problem when you reach 15' you have already done your 1 minute at 30' & 20' so all you are blowing off is the 1 minute at 10'.

It depends on the problem... You're going to have time based problems [OOA], and you're going to have pressure based problems [insufficent weight]. I don't know all the things that could go wrong, and how you would categorize them, if they are timed based, or depth based.

However... lets assume time based: That means with a 30 ft/min ascent rate, you arrive at 30 fsw 4 minutes prior to surfacing. The 'safety stop' diver arrives at 15 fsw 3:30 prior to surfacing. If the problem occurs at T-3:30, then you've gotten 30 seconds of decompression at 30 fsw. However, you've also done 30 seconds of offgassing in the ascent from 30 to 15.

Now when the problem occurs, it will take twice as long to get to the surface from 30 than from 15... so depending on the problem, that may be a factor.

So my current feeling on the matter is 6 of one, 1/2 dozen of the other.

Now I will submit that my way is the best... I do both if I'm ahead of schedule on my gas management calculations...[well, 1@40, 1@30, 15 for 3 + time to boredom or crowding]

 

[mddolson]

Does the benifit out ways risk.?
Clearly stops are a bennifit in deco dives.
DAN research dives utilizing slow ascent rates (ie 10 ft/minute, as apposed to 30 fpm with stops,) bent some volunteers.

DAN dopler research supports the 15 ft safety stop, reducing silent bubbles after dives. The 15 ft stop was selected as a compromise between 10 and 20 ft stops to reduce problems associated maintaining depth.
In heavy seas (6 ft or greater swells) there is a real risk of lung expansion injury at the 10 ft stop. Not one I'd like to expose a novice to.

Is there similar data to support the 30, 20, 10 ft stops on NO-DECO dives ?

This requires a fundamental change by the sport diving agencies, from teaching No Deco stop diving with a safety stop to all dives requiring minimum 3 stops.

Mike D
:blfish:

 

[The Iceni]

Zept once bubbled...
Unless the problem is caused by reaching 5m/15ft (expanding wetsuit?)

Is there really so much potential bouyancy in a wetsuit alone, Zept?

(Since, sadly, this thread seems to have degenerated into point scoring you understand!ut: )