Safety Stop

[1_T_Submariner]

As mentioned before a safety stop from my understanding means that you are not ascending if you are moving horizontally at 15 ft then I would think that would be ok. The people I dive with routinely do this. Just my $.03

 

[TSandM]

At the risk of inciting riot, I have to say that I really like the way GUE approaches this whole issue. Their perspective is that all dives are decompression dives, in the sense that all dives involve nitrogen loading and off-gassing, and therefore all dives should be thought about in the same way -- How much nitrogen have I loaded, and how much time should be spent, and where, to lower that load safely?

If you use that framework for your thinking, you're going to behave rationally. For example, one of the dives I just did in Maui involved swimming out along a reef wall at 35 to 40 feet, but then returning over the top of the reef, with some of that time spent literally at 4fsw. We went down to about 10-15 feet for the swim in to shore, after we cleared the reef, because it was smoother there. Would it have made any sense to do a stop on that dive? Of course not. Spending 20 minutes at 4 to 10 fsw was more than enough "stop" for the minimal nitrogen loading that occurred during the 35 - 40 fsw period.

On the other hand, earlier in the week, we had done a dive to max depth 100fsw, come up (with stops), done an appropriate surface interval, and gone down to a second dive to 85 fsw. Want to bet I did stops at 50% max depth and then full "minimum deco" plus on the way up? Clearly, this was a nitrogen loaded situation, and the more time spent shallow on that dive, the better off I was going to be.

There is actually a lot of logic that can be applied to the broad outline of what you should do under a given set of circumstances, even if you can't nail down the precise parameters of how deep for how long, or exactly where the stops should be made, or how long they should be. It's Uncle Pug's "How I survive without a dive computer" concept.

 

[lowwall]

That is not accurate. Nowhere in the OW curriculum (and not to be wet blanket, but it aint just PADI, btw) does it say that you have to do a safety stop at all times.

The material clearly states that a safety stop is recommended for additional safety --> which is fine. It also clearly indicates that the safety stop is mandatory (a rather unfortunate turn of phrase, but I think most of us can figure out what they mean) when you get to within 3PGs of the NDL.

Nowhere did I state that the OW curriculum always requires a safety stop. I said they substitute a couple of rules of thumb (which I believe you have accurately summarized) for sufficient "information on decompression to allow a diver to make informed decisions on safety stops."

Let me put this another way. Reading through the Ask Dr. Deco forum, it's clear there are are a whole bunch of factors to take into account when deciding whether you would be better off taking 0, 1 or more safety stops. PADI doesn't address any of these, they simply reduce the decision to 1) you must if you went into the grayed out areas of the tables and 2) you should the rest of the time.

Finally, with no further guidance, it's hardly surprising that naive divers have interpreted "a safety stop is recommended for additional safety" to mean everything from "You must stop unless your life would be clearly endangered by doing so" to "Why bother if you aren't doing 5 dives a day?".

Alex

P.S. I'm picking on PADI only because it's the one I know (I'm PADI certifed and I reread the manual when my wife took OW).

 

[miketsp]

30 fpm is hard to understand.
..snip..

I absolutely agree.
Much easier to understand 2 seconds per foot. I don't know why the manuals don't invert it.

 

[OneBrightGator]

If you have suggestions for handling such a situation in a manner that is safer, I'd welcome hearing them.

If they were unfamiliar with the drysuit, then possibly a shallower dive would have been more appropriate. If the issue was weight-related then a proper weight check and erring on the side of heavy would have been in order (possibly even for you). Also, a very conservative dive would be in order, given the possibilities involved with a new drysuit.

With the danger associated with an uncontrolled ascent I don't understand how you'd plan a safe dive expecting that.

 

[jeckyll]

If they were unfamiliar with the drysuit, then possibly a shallower dive would have been more appropriate. If the issue was weight-related then a proper weight check and erring on the side of heavy would have been in order (possibly even for you). Also, a very conservative dive would be in order, given the possibilities involved with a new drysuit.

With the danger associated with an uncontrolled ascent I don't understand how you'd plan a safe dive expecting that.

As you seem so fascinated by a small example I provided of making a slow ascent (an aside really, if you view the original post) I will answer these in order.

1) I said new. New (to me) = having taken the AOW in a drysuit, having borrowed a drysuit on a previous dive (same make and model though slightly larger), having bought a drysuit and making the first dive with it at a familiar site. Which is something like 7 previous drives in a drysuit (perhaps some would classify this as unfamiliar, I would not and don't think I ever said 'unfamiliar'). The discussion pre-dive was a precaution. A low percentage chance. However, I do have a tendency to discuss more contingencies than many (perhaps most) divers I dive with, hence I brought it up and discussed it. It just so happened that this particular problem occurred (didn't the previous dive with the borrowed suit). Good thing we had talked about it upfront.

2) Depth of dive. A shallower dive is always safer. The diver in question had previous dives at this site, in a drysuit, in similar conditions (viz etc), but not this particular drysuit though.

3) This wasn't really an issue of weight (see above on previous dives in same make & model at this site). Weight is rather irrelevant to this circumstance, given that it's the air expanding in the suit and the speed at which it can be dumped from a drysuit that's the issue (I'm surprised I need to point this out). I really don't see when _my_ weight was ever the issue, nor was it referred to. Nor did I believe that I have issue with weight. I can hold at 5 fsw, which we regularly do at this site, with 500 psi with the weight I was diving.

4) Planning of the dive: Dive was planned to max of 60 fsw (short time there, i.e. < 10 min ) ascending slowly to 30 fsw (octo den at 30 fsw, spend a couple of minutes there) then returning to the starting point at 30, ascend to 20 for minimum 3 minutes, from there (an Islet) back to shore surfacing after spending time between 20 -> about 5 feet where we normally surface. Time spent post safety stop dependent on gas consumption. I won't go into other details of our planning which included contingencies for making safety stops on the wall of the Islet, discussion of rock bottom times etc. (i.e. other eventualities).

My final point: You seem to have latched on to one, small, detail in a post that I feel was reasonably well thought out (I'm rather biased on this of course), made a judgement on pretty much no information and then tried to ask questions to confirm your judgement.

Could we have stayed shallower? Yes.
Could you always? Yes.
Would you be safer if you never dove? Yes.
Do I feel that we made significant mistakes in this dives planning? No, I don't.
If I'd _know_ up front some small problem would occur, would I plan it shallower? Sure. Wouldn't everyone?

I'm rather unwilling continue to provide additional data or answer additional questions. If you feel that I'm unsafe (or was so in these circumstances) that's fine, as I highly doubt we'll get the opportunity of diving together. Neither did I propose that others dive as we did for this dive. I did re-read the post of mine that started this discussion and I stand by what I wrote there. I don't think it will lead anyone down a dangerous path. It was after all must my $0.02, not a recommendation of how to dive.

To those reading this thread on the basis of safety stops and their usefulness, I appologize for getting this far off the topic.

Bjorn

 

[dumpsterDiver]

OneBrightGator, I pick up a critical tone as well.

When I was first diving, I had a lot of buoyancy problems. I blew a lot of stops. I knew in advance that it was likely. Anybody I dove with got told that. What should we have done, planned that anybody diving with me should put themselves at the same risk I was taking? I remember one dive where I corked and my buddy sat at 20 feet for a minute, and ten feet for a minute -- I could see him, he could see I was okay. I didn't have any problem with what he did.. . .

I would be interested to know how your instructor taught you to do a safety stop. I learned a long time ago that when beginning divers (or ones that are out of practice) try to ascend in open water (without an ascent line or visual reference) that a high percentage (say 30%) lose control of their bouyancy when trying to make the stop at 15 feet. I found that if I always modified the dive plan to say we are gonna stop at 30 feet for an initial stop of 1 minute, it made a huge reduction in accidental ascents. When attempting to make the 30-ft stop, many divers still blew by it, but because they were TRYING to stop at 30, they were almost always successful in getting their bouyancy under control by the time they hit 15 ft or so. (In other words, they end up doing the officially recommended safety stop).

I found that when these same type of divers try to stop at 15 feet, the very rapid pressure change above 15 feet just overwhelms them. I worked as a divemaster for years and one day I explained the technique of doing a 1 minute stop at 30 to another very experienced divemaster. He was skeptical, but began to try it. Within a week he came back to me and was very surprised how well it served to prevent blow-ups.

And while I think of it, another benefit is that if you do have a problem buddy and you are very close and very watchful, when you see them start to blow through the 30 ft stop, you can just grab them, exhale very fast and this will often be just enough interaction to slow their ascent, remind them of the stop and give them an extra moment to dump some air (all without really bruising their pride). Trying to do the same at 15 feet for the person is just so much harder because of the rate of bouyancy change.

I would still do the normal stop at 15 feet, but if you get them to totally stop and chill at 30, the super slow ascent to 15 feet is much much easier.