Swimming to Surface Question

[M.HARDY]

I aggree with Team Casa...I see no problem with a safety stop unless you're low on air like I was myself once..I spent the rest of the day wondering if iwas headed foeDCS...once was enough for me
M

 

[Thalassamania]

I was responding to someone who said that if a table shows a mandatory safety stop, it is a decompression dive. From your remarks, I conclude that PADI's mandatory safety stops are lawyer-ese and have no statistical influence as long as we follow the ascent protocol carefully.

Safety stops were not part of the design of the RDP, however, since decompression is a statistical problem, you do decrease the odds of being being bent (OK, from tiny to infinitesimal).

From this, I conclude that you can take one of two roads:

• You can say that all PADI NDL diving is no decompression diving , even if a "mandatory" stop is indicated, because the mandatory stops are hokum, or;
• You can say that all diving is decompression diving, and that even if you ignore the stops added by lawyers you still must follow an ascent protocol and not bolt for the surface.

All divng is decompression diving. Just a few seconds at an ambient pressure greater than the surface means that when you return to the surface you will outgas, or decompress. If you bolt two feet at a rapid rate after a few minutes of exposure that will mean nothing with respect to DCS. The closer you get to "no decompression limit" the more things like proper ascent rate can come into play. Your ascent (at a defined rate) is part of the decompression model and exceeding that rate, when you get close to the mathematically defined limit, can get you bent even if you are on the "safe" side of the limit. On the other hand, you can greatly exceed the design ascent rate you are no where close to that limit with relative impunity.

I have learned to take the latter line of thinking. Thanks to your clarifications, I see that the PADI tables are not well-mapped to any contemporary understanding of decompression. (That doesn't really surprise me given everything I have seen, heard, and read so far in my short diving career.)

The PADI RDP is well designed for what it is intended to do. It can be used with relative safety within its design limits. One of the design criterion was a 60 fpm ascent, but substituting a 30 fpm ascent, whilst breaking the design criterion, is unlikely to present any danger as long as the extra time is added to your bottom time.

Touching on another argument in this thread, I agree that given the choice of drowning at depth or risking DCS at the surface, risking DCS is the better choice. That being said, I am wary of false dichotomies. Specifically, I am wary of assuming that just because bolting to the surface and risking DCS is far more acceptable than drowning, that it must somehow be an acceptable strategy for managing emergencies in recreational diving.

Bolting to the surface, while perferable to death due to drowning, is a fam animal stupid approach to solving problems that can easily be dealt with by proper planing, modest skill mastery and/or a tiny bit of team work.

There are tons and tons and tons of things we can do to avoid putting ourselves in the place where those are the only two options, from skills development and training to partner selection to practices in the water to gear selection to gear maintenance to gas selection to gas management to... the list of ways to avoid bolting to the surface as a last resort goes on and on.

True, true.

I am humbled by the depth of knowledge you have shared with us and the clarity with which you have explained the history and reasoning behind the "safety stops." But I don't want to get distracted from a fundamental issue, which is that single tank, recreational, open water diving is still overhead diving.

I don't see it that way. Diving well inside the no-D limits is not overhead diving, though you will outgas on ascent. The closer you come to the no-D limit the more critical control you must exercise concerning your ascent rate and the higher the probability of being bent if you exceed the predefined rate.

I agree with Team Casa...I see no problem with a safety stop unless you're low on air like I was myself once..I spent the rest of the day wondering if iwas headed foeDCS...once was enough for me
M

There is no problem with making a safety stop, but never be afraid to blow though a safety stop. One of my other rants has to do with the stupidity of having to arrive back on the boat with a certain pressure in the tank. My preference is to come up to ten or fifteen feet where I can see the ladder and and watch the other divers or the pretty fish while I blow my tank down to a couple of hundred PSI ... face it the air does your spine no good when it remains in the tank (but it does piss the Divemaster off, even when you tell him what you intend to do).

 

[Reg Braithwaite]

My preference is to come up to ten or fifteen feet where I can see the ladder and and watch the other divers or the pretty fish while I blow my tank down to a couple of hundred PSI ... face it the air does your spine not good when it remains in the tank (but it does piss the Divemaster off, even when you tell him what you intend to do).

Brilliant! And what's the big whup on the first of a two-tank dive, knowing the boat needs to hang around for a surface interval? Seems to me this shouldn't bother the DM in the slightest.

 

[Thalassamania]

Brilliant! And what's the big whup on the first of a two-tank dive, knowing the boat needs to hang around for a surface interval? Seems to me this shouldn't bother the DM in the slightest.

There are lots of folks in the world who are more comfortable obeying rules than they are understanding concepts. This gets back to our discussion of Novice, Beginner, Competent, Proficient and Expert.